X-ray image intensifier tube with secondary emission multiplier tunnels constructed to confine the x-rays to individual tunnels

ABSTRACT

This invention relates to image intensifiers of multiplier type and which are especially useful for X-ray images. The novel device is characterized by construction in which each of the discrete X-ray beams corresponding to individual image points strikes the multiplying channel and is prevented from impinging in addition on adjacent multiplying channels. It is found that in order to accomplish this objective the lateral deviation of said multiplying channels between their entrance apertures and their exit apertures cannot exceed l mm.; and in addition that the difference of the level of said entrance apertures and said exit apertures cannot exceed 1 mm.

tlnited Mates Patent [72] Inventor Edward lEmnnuel Sheldon 30 lists!30th Street, New Yorlt, NY. 10016 [211 App]. No. 796,507 [22] Filed Jan.20, 1969 [2 3] Continuation-impart of Ser. No. 519,814,

Nov. 26, 1965, Pat. No. 3,461,332

[45] Patented Sept. 7, 1971 [54] l t-111111 lit RAGE ilN'lllENSll llElRTlUfiE WllTlll SECONDARY EMHSSIIUN MULTHPLHEIR TUNNlElLS CONSTRUCTEID T0CONIFME THE Ell-RAYS T0 lllDlli/IIDUAL TUNNIElLS 10 Claims, 414 DrawingFigs.

[52] 1.1.8.0 313/65, 313/82, 313/105, 250/213 [51] lint. Cl ..ll101j29/68, 1101 13/23, HOlj 31/26, HOIj 31/50 [50} Field ofSenrclh3l3/94,92, 106, 104, 105, 65, 94; 250/213, 63

[56] References Cited UNlTED STATES PATENTS 2,879,406 3/1959 Wachtel250/213 2,996,634 8/1961 Woodcock 313/92 3,237,039 2/1966 Fyler 313/923,461,332 8/1969 Sheldon 313/65 Primary Examiner-Roy Lake AssistantExaminer-V. Lafranchi Attorney-Polachek & Saulsbury ABSTRACT: Thisinvention relates to image intensifiers of multiplier type and which areespecially useful for X-rays images. The novel device is characterizedby construction in which each of the discrete X-rays beams correspondingto individual image points strikes the multiplying channel and isprevented from impinging in addition on adjacent multiplying channels.It is found that in order to accomplish this objective the lateraldeviation of said multiplying channels between their entrance aperturesand their exit apertures cannot exceed 1 mm.; and in addition that thedifference of the level of said entrance apertures and said exitapertures cannot exceed 1 mm.

PATENTEU SEP 71971 3,603,828

SHEET 1 [M II-RAY IMAGE IN'IFNSII IEII 'I UIIIIE WI'I'III filECONDAIRIIlEl /IISSIGN MULTIIPLIIEII TIUNNEIJF ICGNSTIIIJCTIED T CONFINIE TII-IIEII-IIAIIS T0 INDIVIDUAL TUNNIELS This invention relates to the imageconverters and image intensifiers for various radiations and especiallyfor the use with X-rays or neutrons and to be used independently or incombination with television camera tubes, and represents a continuationin-part of my copending U.S. Pat. application Ser. No. 519,814, filedNov. 26, 1965, now U.S. Pat. No. 3,461,332 issued Aug. 12, 1969, andwhich is a continuationin-part ofU.S. Pat. No. 3,400,291 filed Aug. 28,1964. In addition the instant application has common subject matter withmy U.S. Pat. No. 3,279,460 filed Dec. 4, 1961 and issued Oct. 18, 1966;with U.S. Pat. No. 3,149,258 filed Sept. 9, 1954 and issued Sept. 15,1964; with U.S. Pat. No. 3,021,834 filed Nov. 28, 1956 and issued Feb.30, 1962; and with U.S. Pat. No. 2,877,368 filed Mar. 11, l954issuedMar. 10, 1959.

My invention will be useful in all situations which require theconversion of radiation from one wavelength to another wavelength ofspectrum.

My invention will be useful also for intensification of the brightnessof the images to be reproduced.

In addition, my invention is of great importance for improvement ofresolution of images reproduced.

In addition, my invention will make it possible to miniaturize thepresent image converters, and image intensifiers, such as are describedin my U.S. Pats. Nos. 2,555,423 and 2,555,424; and which are used in thefield of diagnostic radiology.

My invention will be better understood when taken in combination withthe accompanying drawings.

IN THE DRAWINGS FIG. I shows the novel image intensifier.

FIG. Ia shows novel electron guide.

FIGS. Ib, 11c, Id, lie, and llfshows modifications of the electronguide.

FIGS. 2, 2a, 3, 4 and 5 show modifications of the image intensifier.

FIGS. 7 and b show cascade image intensifiers.

FIGS. 6 and do show the use of two tubes in cooperative relationship.

FIGS. 9, III and Mia show a novel composite screen.

FIGS. Ill and 112 show image intensifier provided with a fiber-opticlens.

FIG. 13 shows a novel television camera tube.

FIGS. 113a, 113b, III: shows novel acoustic image converters.

FIG. I4 shows a novel electron gun.

FIG. 115 shows a novel storage tube.

FIG. 115a shows a novel curved electron guide and multiplier.

FIG. 15b shows a modification of the novel curved electron guide andmultiplier.

FIG. 1150 shows a novel spiral electron guide multiplier.

FIG. 115d shows image intensifier tube.

FIG. I6 shows a novel X-ray image intensifier.

FIG. 117 shows a neutron image intensifier.

FIG. 1171; shows a modification of neutron image intensifier.

FIG. 118 shows a novel infrared image intensifier.

FIG. 118a shows a modification of infrared image intensifier.

FIG. 19 shows an image-intensifying tube with angulated type of electronmultiplier.

FIG. I90 shows modification of the angulated electron multi lier.

FIG. IIIIb shows a vacuum tube with a curved-type electron multiplier.

FIG. 20 shows a novel television pickup tube with electron multiplier.

FIG. 211 shows a vacuum tube with a novel electron multiplier offiber-optic type.

FIG. 211a shows a modification of the device shown in FIG. 211.

FIG. 22 shows a novel image tube with a perforated imagereproducingscreen and using reflected electron beam.

FIG. 22a shows a modification of the device illustrated in FIG. 22.

FIG. I shows a novel vacuum tube which comprises a photoemissivephotocathode 2 such as of Cs, Na, K with Sb, Bi or As or of a mixture ofaforesaid elements, such as KCsSb or NaKSb. For infrared radiation CsOAgor CsNaKSb will be more suitable. The photocathode 2 may be deposited onthe end wall of the tube 1 or on a transparent supporting plate such asof quartz, glass or mica 3 or of arsenic trisulfide. The visible orinvisible radiation image of the examined object 4 is projected by theoptical system 4a on the photocathode 2 and is converted into a beam ofphotoelectrons, having the pattern of said image. The photoelectron beamhas to be focused in order to get a good reproduction of the image. Inthe devices of the prior art, he focusing was accomplished byelectrostatic or electromagnetic lenses which are large and heavy. As aresult, the standard image tubes are bulky and cannot be miniaturized.In my device, I eliminated the electrostatic or electromagnetic lenseswhich made it possible to make a miniature device. The problem offocusing the electron beam without the use of electron-optical devices,was solved by the use of a novel mechanical device such as the aperturedguide 5. The guide 5 comprises a plurality of tunnels 6, each tunnel isof microscopical diameter and extends through the whole length of theguide. Each of the tunnels must be insulated well from the adjacentones. It was found that there are various ways to construct such guide.In one preferred embodiment the guide 5A may be constructed of aplurality of hollow tubes 15 of glass or of plastic, having their bothends open and being of 10 microns diameter or less, and held together bysilicone or other temperature-stable plastics. or by fusing themtogether by heating, see FIG. lla. For a good resolution of the image, Iuse ISO-250,000 of such tubes stacked together in one-square-inch area.In some cases each of tubes I5 is coated on inside walls with aconducting layer, such as of aluminum, 7a or semiconducting layer 7c,which is connected to an out side source of electrical potential.

The tubes 15 may be also held in position at their ends only either byfusing them at the ends only, by heat, or by gluing them together withsilicone or other plastic material compatible with vacuum, ormechanically, for example, by threading their ends only into a meshscreen mounted rigidly in the tube.

In cases in which resolution of images is not important, the guide 5 maybe constructed of a number of apertured glass plates combined in oneunit as was described above for tubes 15. In the preferred embodiment ofinvention the tubes 15 of glass or plastic may be coated on theiroutside walls with a conducting material 701 or semiconducting material7c and next with the insulating material such as of fluorides, glass,plastic, MgO, or silicon oxide 50, extending along the entire length ofsaid tubes and around their entire circumference. Next the inner glassor plastic wall of the tubes 15 is leached out to make the conducting 7aor semiconducting or resistive layer 7c face the lumen of the tunnelsI5. In this construction the insulating coating 50 is of materialresistant to the leaching agent and it will serve as a support for otherlayers. The material for uniting the tubes should be resistant totemperature necessary for vacuum processing. Plastic material such asfluorocarbons, polyethylenes such as fluoroethylenes or siliconcompounds such as silicates are useful.

If the tubes I5 are united by heating them, the outer walls of the tubesmay be clad before the fusion with a glass or other material which isresistant to the leaching agent and which melts easier than the layer50. In some cases the dielectric layer 50 may serve for this purpose aswell.

In some cases, the first coating to be applied to the walls of the tubes115 may be of a secondary electron emissive material 2%, as shown inFIG. Id, which may be of semiconducting type such as CsSb, of insulatingtype such as of fluorides, MgO, or allcali halides such as KCI or ofaluminum oxide, or of conducting type such as He, Ni, Cu, or of amixture thereof. In some cases layer Sill and 7a or 70 should be able totolerate temperature of 600 C. The dielectric layer 50 as was explainedabove serves as a support for all other layers and extends along theentire length of the tunnels.

The secondary electron emissive layer 20 should preferably extend alongthe entire length of the tubes and cover the inside lumen of tunnels 6on all sides.

In some cases the coating 20 may be also applied to the inside walls ofthe tubes 15, after they have been coated with the conducting andinsulating layers and after they were leached as was described above,but the results are inferior than in the method described above.

It is also possible to coat the inside walls of the tubes 15 with aconducting layer and with a secondary electron emissive layer 20 byevaporation or electrolytically. In such case the tubes 15 do notrequire any leaching at all. The results however are inferior to themethod described above because the secondary electron emissive coatingis not uniform. In my preferred construction the deposition of thesecondary electron emissive material is done on the external surface ofthe walls of said tubes which makes it practical to produce a homogenousand uniform deposition of the secondary electron emissive material. Aswas explained above the subsequent leaching of the glass makes thesecondary electron emissive material face the lumen of the tunnels 612.

Another preferable method of building the guide 5 is to use a fiberplate which consists of plurality of fibers of 5 to microns diametermade of glass or plastics.

The fibers are coated with a dielectric material 50 such as a suitableglass, plastic, fluorides, silicon oxide or other silicon compounds, asshown in FIG. 1f. In some cases the fibers and their coating should beable to tolerate temperature of 600 C.

The material for uniting the fibers should be resistant to leachingagent used for the glass and also resistant to temperature necessary forvacuum processing. Among plastic materials fluorocarbons, polyethylenessuch as fluoroethylenes or silicon compounds are the best. All thesefibers are glued together chemically or are fused together by heating,Such a fiber plate is now subjected to a leaching process in which theglass or plastic fibers are etched out and dissolved by a suitablechemical. The leaching agent does not attack however, the coating offibers. We will obtain therefore, after the leaching is completed, aguide 5F having as many tunnels 6 as there were original fibers in theplate. The fiber plates can be constructed of fibers having only 6microns in diameter. Therefore the tunnels 6 will have a diameter ofapproximately 6 microns. If it is important to have the tunnels of auniform diameter, the fiber plate should be made of fibers which have acoating of glass or plastic which does not deform during the heatingfusion. In some cases it is preferable to have an electricallyconducting coating on the inside walls of tunnels 6. In such case, alayer of Al, Pd, Au or Ag may be deposited on the inside walls of thetunnels 6 either by evaporation or electrolytically. A preferred methodof providing a conducting 7a or semiconducting or resistive 7c coatinginside of tunnels 6 is to use the fiber plate in which the fibers beforecombining them in one unit are clad with a metallic coating or in whichthe dielectric coating such as of glass or plastic comprises a metal. Insuch case an additional insulating layer 50 which may be of a glass,plastic, fluorides or silicon oxide or silicates should be depositedoutside of the metallic layer to provide a good electrical insulation oftunnels 6 from each other. It should be understood that tunnels 6 andall their modifications have the length a few times, which means atleast 2 times, larger than the diameter of their apertures 42.

Also fiber-optic mosaics may be used for construction of the electronguide 5. Such mosaic can be made of a plurality of fibers, having a coreof one kind of glass and a coating of another type of glass. All thesefibers are fused together by heating. Such a fiber-optic plate is nowsubjected to a leaching process in which the core of the fibers isetched out and dissolved by a suitable chemical. The leaching agent doesnot attack however, the coating of fibers. We will obtain therefore,after the leaching is completed, a plate having as many tunnels as therewere original fibers in the fiber-optic mosaic. It should be understoodthat these glass fibers and fibers described above may be also providedwith a coating of secondary electron-emissive material 20 and of theconducting material 7a before being coated with another type of glass.Therefore after the core of said fibers is leached out the secondaryelectronemissive layer will face the lumen of tunnels 6.

I found that the tunnels made of the metal tubes in the prior art couldnot give a good resolution of the images because the metal tubes couldnot be made of diameter smaller than 0.50 mm. and could not bereproduced uniformly. In my device glass or plastic tubes are used whichcan be produced of diameter of0.01 mm. and which can be produced with agreat degree of uniformity in great numbers. My device will need 200,000tubes or more.

It should be understood that the work glass in the specification and inthe claims embraces all kind of glasses and synthetic plastic materialsas well.

Another electron guide is shown in FIG. 10. The vacuum tube 1A has asource of electrons such as photocathode 2 or an electron gun 40 and anovel electron guide 5C.

The guide 5C comprises in vacuum tube 1A a plurality of perforatedmembers 60 such as plates or meshes of dielectric material, such asglass or plastic and a plurality of electrically conducting perforatedmembers 61 such as plates or meshes of steel, nickel or copper. Thedielectric members 60 and conducting plates or meshes 61 are stackedtogether and glued together or fused in an alternating pattern. In thisway plural tunnels 6a are produced which have walls of alternatingstrips of dielectric material and of a conducting material. Allelectrically conducting members 61 may be connected to an outside sourceof potential.

An improved method of producing apertures plates or meshes is to use afine-focused electron beam for perforating continuous sheets of suitablematerials. This method is used for electrically conducting materialssuch as nickel, copper beryllium and for dielectric materials such asplastics, fluorides or glass as well.

In some cases it is advantageous to intensify electron beam by asecondary electron multiplication. This is accomplished in my inventionby coating the perforated apertured conducting members 61 of the guide5D in vacuum tube 18' with a secondary electron emissive material 20asuch as calcium fluoride, alkali halides, such as KC], aluminum oxide,CsSb, and Ni or Be, of the thickness of 50 to 250 angstroms as shown inFIG. 1b. This coating 2011 may be deposited by evaporation or byelectrolytic process, and is deposited before the members 60 and 61 arecombined together in one unit, their apertures being aligned and formingthereby elongated tunnels 60 having the length larger than diameter ofsaid apertures. It should be understood that the various arrangements ofdielectric members 60 and of conducting members 61 coated with layer 200come withing the scope of my invention. For example, I may use a fewdielectric members 60 for each conducting member. The conducting members61 coated with the layer 20a are connected to an external source of theelectrical potential. Each member 61 is provided with a potential a fewkv. higher than the preceding one. In the vacuum tubes of the prior artthe emitted secondary electrons had to be focused by means of bulkymagnetic devices to prevent loss of resolution. In my device, allelectron-optical focusing devices can be eliminated and still a betterresolution is obtained than in the prior art. The secondary electronsmust travel through the tunnels 6a and are restrained to the size ofsuch tunnels. The tunnels 6a or 6 should preferably be in some cases atan angle to the photocathode 2. In some cases the apertures 42 oftunnels 6 or 6a should have a bevelled shape.

It was found however that the perforated plates of meshes whether ofconducting type or of dielectric type cannot give as good resolution, asthe electron guides made out of hollow tubes or of fibers which weredescribed above. It was also found that conducting mesh screen coveredwith insulation and stacked together do not make tunnels of uniformdiameter and shape as it is required for the best resolution of theimages as it is impossible to bring plurality of such screens into aperfect registry with each other as it was successfully done in electronguides using hollow tubes or leached out fiber plates.

My novel imaging device may use all embodiments of the electron guidesdescribed above. The novel image tube ll shown in FIG. 1, as describedabove, has the photocathode 2, on the support 3, electron guide 5 and animage-reproducing screen 8. The image-reproducing screen 8 comprisesluminescent or electroluminescent material such as ZnSCdS, ZnSAg or zincsilicate and is covered on one side with an electron-transparent,light-reflecting layer 9 such as aluminum. The layer 9 prevents thelight emitted by the screen d to scatter back to the photocathode 2. Theimage of the examined area 4 is projected by the lens 4a on thephotocathode 2 and is converted into a beam of photoelectrons having thepattern of said image. The photoelectron beam is accelerated by theelectrical fields 39, enters the guide 5 through the apertures t2 and isfocused by said guide onto luminescent screen 8. It leaves the guidethrough the apertures 42a, is accelerated again by the fields 39,strikes the screen d and reproduces a visible image therein. This novelimage tube does not require any electron-optical focusing devices forgood resolution of the image.

I found that the closer the guide 5 is to the photocathode 2, the betteris the resolution of the image. In particular, a distance of a smallfraction of 1 millimeter will give the best results, the distance of afew millimeters will give a much worse resolution. The vacuum tube 1shown in FIG. 1 must be provided with a unidirectional electricalpotential for acceleration of photoelectrons from the photocathode tothe guide 5, and from the guide 5 to the image-reproducing screen 8. Theaccelerating potential may be applied to the conducting cylinders whichtransmit electrons or coating 39 on the inside of the tube envelope orto the conducting layer 7 such as of aluminum. The higher theaccelerating potential is, the brighter the reproduced image will be inthe screen 8. There is, however a limit to the strength of theaccelerating potential which is set by the dielectric strength of thetube. The use of guide 5 allows the potential to be spread between thephotocathode 2 and screen 8 over a longer distance and without loss ofresolution. Therefore it will be possible now to use, in the tube 1, amuch higher potential than it would be feasible without said guide 5.The conducting layer 7 maybe 50-400 A. thin so it will be completelytransparent to the photoelectrons emitted by the photocathode 2. Theconducting layer 7 or semiconducting layer 70 is connected to an outsidesource of potential and may be preferably in contact with the conductingor semiconducting coating on inner walls of tunnels 6. The layer 7 maybe continuous. ln some cases, a perforated metallic layer 7b will bebetter. The perforations in the layer 7 corresponding to the apertures42 of the tunnels 6, may be made by blowing a strong current of airthrough the tunnels 6. Another method of producing the aperturedconducting member is to use a perforated plate or mesh screen ofconducting material such as 43 describedbelow.

The length of the tunnels 6 in the guide 5 must be longer than thediameter of the apertures 42 of said tunnels. The actual length willvary according to the application of my guide and the type of vacuumtube. However the tunnels of the guide should be at least a few timeslonger than the diameter of the apertures. The longer is the guide 5,the greater difference of potential can be applied to both sides of saidguide. The greater is the the difference, the more acceleration of theelectrons can be achieved. This brings about a greater imageintensification, which was one of the purposes of my invention. Theacceleration potentials may be supplied from an external source ofpotential connected to the layer '7 or 413 or to separate grids whichtransmit electrons and are disposed on both sides of the guide 5, or toconductive rings 39 mounted on the walls of the vacuum tube. In thedevices of the prior art, it was impossible to provide a large potentialdifference, because the separation of the fluorescent screen a from thephotoelectric screen 2 could not be longer than 0.25-0.5 cm.; exceedingthis distance caused a prohibitive loss of resolution of the image. Inmy device, in spite of the elimination of the focusing electron-opticallenses or fields, l can provide separation of the photocathode 2 and ofthe fluorescent screen 8 of any desired length without a loss ofresolution of the image. I found that for the best resolution in thisembodiment ofinvention the walls of the tunnels 6 facing the lumen ofsaid tunnels should be free from a photoelectric material or from asecon dary electron-emissive material.

The electron beam from the photocathode 2 carrying the image istherefore guided by the electron guide 5 to the imagereproducing screenill. It is accelerated to impinge on said screen 8 with a sufficientvelocity to produce therein a visible image of increased brightness.

The tunnels 6 may be uniform in their diameter through the whole lengthof the guide 5. The tunnels 6 may have also a divergent form, in whichthe exit apertures are larger than the entrance apertures. In such casethe electron beam will be enlarged upon its exit from the guide. Thetunnels 6 may be also of a convergent form in which the exit aperturesare smaller than the entrance. In this case the electron beam will bedemagnified on its exit from he guide.

The separation of guide 5 from the photocathode 2 will cause somephotoelectrons to strike the solid parts of guide 5, instead of enteringthe apertures 42 in the guide. In this way, a space charge may beproduced on solid parts of guide 5,which may interfere with thephotoelectron image. I found that development of the space charge is thecause of failure of such devices. The conducting layer 7 will preventthis from happening as the charges will be able to leak away throughlayer 7. In some cases, it is preferably to mount guide 5 in contactwith the photocathode 2 or the photocathode may be deposited directly onthe end face of guide 5 instead of on the end wall of the tube or on asupporting member 3, as is shown in FIG. 2. In this construction theconducting layer should be a perforated layer 7b or a perforated member43. The discontinuous electrically conducting layer 7b may be also madeby evaporation and will have -90 percent transmission for electrons. Insome cases it is preferably to use an electrically conducting member 43in the form of a metallic wide-mesh screen or perforated plate ofmetallic material or of a perforated member coated with an electricallyconducting; material such as tin ox ide. The member 43 is mounted on theend face of the guide 5 in such a manner that openings of the screen orplate 43 coincide with one or with a few apertures 42 of the guide 5.The screen or mesh 13 is connected to an outside source of electricalpotential in the same manner as layer 7b. In this construction I foundthat a problem arises because of the chemical interaction between thephotoemmissive material of photocathode 2 and the materials of guide 5.It is important therefore to select materials which do not poison thephotocathode. Lanthanum glass is chemically compatible. Still aprotecting separating layer 20 of a light transparent material such asof calcium fluoride, MgO, or of silicon monoxide may be needed. Thelayer 2a should be preferably perforated and have a transmission forphotoelectrons of 80-90 percent. The apertures of the layer 20 mustcoincide with the apertures 42 of the guide. The layer 2a may beprepared by deposition on the top of the layer 43 of a continuous layerfirst and next by rupturing said layer with a strong current of airblown through tunnels 6, so that only the parts overlaying the solidportions of the guide 5 will remain in position.

Also, the phosphor screen b may be deposited directly on the end face ofguide 5. This construction facilitates markedly the construction of tube11, as guide 5 with the imagereproducing screen 8, and in some casesalso with the photocathode 2 may be prepared outside of vacuum tube 11,and then introduced into tube in in. one unit, and mounted therein.

In some cases, either only the photocathode 2 or only the image screen dare in contact with the guide 5. In case the screen 8 is separated fromthe guide 5, the separation, for the best results, should be preferablya fraction of l millimeter.

In some cases it is preferable to prevent the electrons which travelthrough the tunnels 6 or 6a in the guide from striking the walls of saidtunnels. This can be accomplished by providing the walls of said tunnelswhich face the lumen with a conducting or semiconducting coating 7c asshown in FIG. 2a. The conducting coating may be of aluminum or chromium.The semiconducting coating may be of tin oxide or of titanium oxide. Thecoating 7a may be connected to the perforated conducting member 43 or tolayer 7 which again may be connected to an outside source of electricalpotential. As all tunnels 6 are in contact with the layer 7 or withmember 43, walls of said tunnels will have a potential which will repelelectrons travelling through said tunnels.

In some cases, the second perforated member 43 or 7 mounted on theopposite end of the guide 5, may be discontinuous from the coating 7a byterminating said coating 7a before reaching one end face of the guide 5.In this construction, the second member 43 may be connected to theexternal source of electrical potential to provide acceleration forelectrons.

In the embodiment of invention, shown in FIG. 1 and 2, and 2a, thetunnels 6 of the guide 5 run normally to the photocathode 2 and arestraight from the beginning to their end to prevent photoelectrons fromstriking from the beginning to their end to prevent photoelectrons fromstriking the inside walls of the tunnels.

It will bee understood that my device may use a plurality of electrongui'des 5. In such case electron-accelerating means such as grids,rings, cylinders of meshes connected to a suitable source of potentialmay be interposed between the electron guides.

The semiconducting coating or resistive 7c in some cases is preferablyto conducting coating because it allows to establish potential gradientalong the length of the tunnels 6. This potential gradient will causeacceleration of electrons into direction of the exit apertures 4311 ifit is connected to a suitable source of electrical potential.

In many cases it advantageous to intensify electron beam by a secondaryelectron multiplication e.g. by coating the inner walls of the tunnels6a with a secondary electron emissive material such as CsSb, Ni, Be,calcium fluoride, alkali halides such as KCl or aluminum oxide orothers. This coating 20 may be deposited by evaporation into tunnels 6,but the deposition is not uniform for the best results. In a preferablemodification of this invention the secondary electron emissive coating20 for the inner walls of the tunnels 6 may be provided by the methodswhich were described above. The glass or plastic fibers 38 before beingfused or glued into a fiber plate are coated with a secondary electronemissive material 20, such as was described above. On the top of saidcoating 20 an electrically conducting coating 35 is applied, such as ofchromium, aluminum or nickel. On he top of the conducting coating 35, adielectric coating 36 such as of glass, plastic or of fluorides isapplied, which will serve to fuse all fibers into one fiber plate asshown in FIG. 1e. It should be understood that the coatings 20, 35 and36 must be of material resistant to the action of the chemicals used foretching out the fibers. After the fiber plate is prepared, and thefibers are leached out, we obtain the tunnels which have the followinglayers. The layer facing the lumen of said tunnels is the secondaryelectronemissive layer 20, the next layer is the electrically conductinglayer 35, the next layer is the insulating layer 36. The conductinglayer 35 may be connected to the source of suitable potential for thebest secondary electron emission.

In some cases, instead of conducting layer on the inside walls of thetunnels 6 it is better to have a layer of semiconducting material 70such as of tin oxide, titanium oxide, or zinc fluoride. It should beunderstood that the use of semiconducting coating instead of aconducting coating applies to all modifications. In some cases anelectrically resistive evaporated layer 7c may be used instead of asemiconducting layer 70. The resistive layer in a modification of myinvention, instead of being a base for the electron-emissive layer 20,may replace it and serve to provide electron multiplication. In thisconstruction the tunnels 6 should be at an angle to the photocathode orthe photocathode at an angle to the tunnels.

The operation of the modification of my invention using secondaryelectron emissive layer 20 is shown in FIG. 4. The photoelectronsentering the apertures 42 are directed in to said apertures at an angleso that they will impinge on the walls of said tunnels 6 coated withlayer 20.'In this construction apertures 42 are slanted at an angle of45-55 and tunnels 6b in the guide 5 are straight or at an angle inrelation to the photocathode 2. In some cases in order to provide theobliquity for the entering photoelectrons, instead of the tunnels, thephotocathode 2 may be mounted at the angle. In such a case the tunnelswill be normal in relation to the end wall of the tube. The angle atwhich photoelectrons enter will depend on the size of apertures andtheir spacing from the photocathode. The photoelectrons must have only afew-hundred-volt velocity to produce secondary electron emission greaterthan unity from the layer 20. The low accelerating voltage in front ofthe photocathode 2 creates the problem of resolution. As was explainedabove, my device is characterized by the absence of electron-opticalfocusing means. The photoelectrons leaving the photocathodes have arange of velocities 0.5 volts -l0 volts according to the wavelength ofradiation used. The use of 300- to 1,000-volt accelerating potentialrequires a much closer spacing of the photocathode 2 to the end face ofthe guide 5 than devices in which the accelerating potential is a fewthousand volts. It was also found that the use of the low acceleratingvoltage required that the conducting layer 7 be of perforated type suchas layer 7b or a perforated member 43 because electrons of a lowvelocity will not be able to penetrate continuous layer 7.

The inside walls of the tunnels 6 should have a progressively higherpotential along their length in order to cause repeated impingement ofsecondary electrons on the layer 20 while they are traveling to the exitapertures. It was found that the best way to provide progressivelyhigher potential for the walls of the tunnels 6 is to divide theelectron guide 5 into plural segments and to interpose between saidsegments apertured electrically conducting members 43 or apertured layer7b or conducting rings which can be connected to various electricalpotentials required. The conducting layer 7a or semiconducting layer 70which are on each tunnel are connected to said apertured electricallyconducting members. This construction affords a simple and practicalsolution of supplying progressively higher potential to all tunnels 6 inspite of the fact that we may use 200,000 tunnels or more in oneelectron guide 5.

I also found that devices of the prior art failed because ofimpossibility of obtaining an exact registry of the apertures of the endface of one electron guide 5 or one segment of the electron guide withthe apertures of the next electron guide, when many guides are mountedin the tube separately and spaced apart. I found that the best wayregistry was obtained when the electron guide 5 described above was cutinto plural segments to produce plural guides and the conductingapertures member 43 was inserted between the segments of said guide in aproper spacing from them and then all parts were fixed into one rigidunit, either mechanically or chemically or by heating. In some cases theconducting apertures members are mounted only one end faces of thesegments of the electron guide and are not between them in a spacedposition.

The registry of apertures of successive guides I found to be the mainproblem for good definition of images. The best method to accomplish agood registry is as follows. An electron guide of one of types describedabove is mounted on a support which has a few compartments which can bemoved apart in one plane only. The electron guide 5 is cut to providetwo or more smaller electron guides. The movable parts of the supportare moved apart to separate these segments of the electron guide. Thisprovides the space for the mounting of the electronically conductingmember 43 such as was described above. At the same t ir ne it preventsdisplacement of the segments of the electron guide in relation to eachother in any other plane. The electrically conducting members t3 aremounted either on the end face of the segments of the electron guide, orare mounted between the end faces of said segments. Next the movableparts of the support are moved back. This brings the segments of theelectron guide into a close spacing to each other. In some cases aninsulating spacer in the form of mica ring may be interposed between twoend faces of the adjacent segments of the electron guide. This will beuseful when the apertured conducting members 43 or 7b are mountedbetween the end faces of the segments of the electron guides. Next thesegments of the electron guide with the electrically conducting members43 are fixed into one rigid unit. In this way a perfect registry ofapertures of plurality of electron guides is obtained, which could notbe accomplished in the prior art. The above-described units comprisingplurality of electron guides can be mounted in the vacuum tube withoutany damage to the registry of the apertures.

The plural segments can be united either by chemical means such as by aplastic compatible with vacuum tube processing such as silicones, orfluorocarbons or polyethylenes. The segments can be also joined in oneunit with mechanical means, or by the embedding material or by heatingand fusing them.

It was found that a part of the photoelectrons does not enter intoapertures 42 but strikes instead the solid parts of the guide 5. As thephotoelectrons have velocity at which secondary electron emission ishigher than unity a positive charge will develop around the apertures42. I found that this charge reduces considerably the sensitivity of mydevice. This charge may be removed by mounting on the end face of theguide 5 a perforated electrically conducting member 43 in such a mannerthat its apertures overlie the apertures 42 of he guide. Also perforatedlayer 7b may be used for this purpose. The member l3 of layer 7b areconnected to a suitable source of potential and will be able thereforeto remove the space charge. It was found that a continuous electricallyconducting layer 7 could not be used in this device because the velocityof electron was not sufficient to penetrate through it. The electronsmake the exit through the apertures at the end of the electron guide 5.They are accelerated to a high velocity and strike the image-reproducingscreen 8 through the layer 9. It should be understood that themultiplied electron beam after its exit from the guide 5 may be alsoused in combination with other devices such as targets of televisiontubes, storage tubes, and other vacuum tubes.

My construction will therefore produce a device which in spite of itssmall size is capable of a high image resolution. In addition my devicewill be very rugged mechanically. In addition my device will reduce thefield emission in the vacuum tubes arising from the spreading of caesiumvapors.

In another modification of my invention using secondary electronemission for intensification of the images the secondary electronemission for intensification of the images the secondary electronemissive layer 20a is used on the end face of the guide 5 as it is shownin FIG. 5. It is preferable to deposit first layer 20a whether it be inthe form of a continuous layer or in the fonn of a discontinuous layerand then to mount on it electrically conducting member 7 or M whichtransmitting to electrons as shown in FIG. 5. In some cases the sequenceof the layers 20a and of the member d3 may be reversed and the member 43is the first one to be mounted on the end face of the guide. Thesecondary electron-emissive layer 20a in this embodiment of inventionmay be deposited as a continuous layer or as a discontinuous layer whichcovers essentially only the apertures 4l2 and the edges around them. Itshould be understood that in cases in which the fragility of this deviceis not critical the layer 200 and the member d3 supporting it may bemounted spaced apart from the end face of the guide 5E. They must behowever very closely spaced in relation to said end face so that thesecondary electrons will enter the apertures 42 without causing loss ofresolution. The spacing smaller than 0.1 cm. will be necessary for agood resolution.

The secondary electron-emissive members 2.0a are as thin as 50-250angstroms so that they will emit secondary electrons in forwarddirection when impinged by primary electrons of sufficient velocitywhich may be a few kv. The secondary electron-emissive member 200 may beof a conducting material such as copper, beryllium or nickel and theymay be connected directly to the source of potential. The same is trueabout members 2011 of semiconducting materials such as caesium-antimony.If however the secondary electron-emissive material is of dielectrictype such as fluorides of calcium or magnesium aluminum oxide, or alkalihalides, such as KCl, a conducting layer continuous or apertured shouldbe provided as the base for said electron-emissive member 20a. It wasfound that the use of dielectric type of secondary electron-emissivemember gives superior results to the devices which use a conducting typeof secondary electron emitter.

It was found that the device described above serious difficulties arisebecause of the development of space charges. The velocity ofphotoelectrons for the best operation of the layer 20a should be a fewkv. The photoelectrons of this energy striking the solid parts or theelectron guide 5 will cause secondary electron emission smaller thanunity. As a result a negative charge will develop and the solid parts ofthe guide 5 around the apertures 42 and will cause various complicationsin the operation of the device. It was found that this negative chargemay be removed by using a continuous type of electrically conductinglayer 7 which is connected to a suitable source of potential, inpreference to the use of the perforated layer 7b or of the member 43.

The guide SE in this embodiment of invention has tunnels 6 normal to thephotocathode 2, the tunnels 6 have no coating 20 of secondaryelectromemissive material or of a photoelectron material, as it wasdescribed above and shown in FIG. 1.

It should be understood that the guide 5E may comprise a plurality ofshort guides, combined in one unit by mechanical means, chemical means,or by heating. Each of short guides is provided with the conductinglayers 7, 7b or 43, and has the secondary electron-emissive layer 20a onone or both end faces.

It should be understood that the guide 5 may be sliced into manyseparate segments, and the secondary electron-emissive screens describedabove may be interposed between the segments of the guide. Next allthese parts may be combined in one unit, either mechanically orchemically or by heating. In this way cascade intensification of theelectron beam by electron multiplication is obtained without any loss ofresolution in spite of the absence of electron-optical focusing devices.

It should be understood that the segments of the electron guide 5provided on end faces with the layer 20a should be spaced apart toprovide sufficient separation for the use of a high accelerating voltageapplied in this device. This spacing should preferably not exceed 0.5cm. to preserve a good definition.

The rest of the operation of the vacuum tube 1B is the same as of thevacuum tube 1. The great advantage of this novel construction resides inruggedness of this device.

It should be understood that the novel electron guide 5E may be usedalso in various vacuum tubes such as television camera tubes, storagetubes, kinescopes etc.

In the devices of the prior art the mesh screens coated with secondaryelectron-emissive layer were necessarily very fragile, because of theirthinness. in my device the layer 20a and member 4l3 or '7 are beingdeposited on the end face of the guide have mechanical strength whichallows the use in all operating conditions. Another novelty of my deviceresides in elimination of electron-optical focusing devices and withoutloss or resolution.

in some cases the end walls of vacuum tube 1 or 1A or llB should be madeof fiber-optic plates 12 and ll2a as shown in FIG. 3. It should beunderstood that this construction applies to all vacuum tubes describedin this disclosure. The fiberoptic plates comprise a plurality oflight-conducting fibers. Each of said fibers consists of a core ofmaterial having a high index of refraction such as suitable glass e.g.flint glass, or

quartz or arsenic trisulfide or plastics such as acrylic plastics suchas lucite or polystyrenes.

The light-conducting fibers should be polished on their external surfacevery exactly. Each of them must also be coated with a very thinlight-opaque layer to prevent spreading of light from one fiber toanother. I found that without said lightimpervious coating, he imagewill be destroyed by leakage of light from one fiber to another. Thelight-opaque layer should have a lower index of refraction than thelight-conducting fiber itself. Such a coating may have a thickness ofonly a few microns. The light-opaque coating maybe of materials such asa suitable glass or plastic. In some cases it is preferable to use glassor ceramics which will tolerate a high temperature such as of at least600 C.

Especially glass or plastic of a lower index of refraction than thefibers and containing aluminum or chromium diffused into them aresuitable materials for the coating.

In another modification the light-opaque layer such as of chromium oraluminum is deposited on the outside of the coating which in such a casemay be of transparent glass or plastic.

All said fibers are glued together with silicones or are fused togetherby heating them to form a vacuum-tight unit. In the use of suchfiber-optic plates, care must be exercised to prevent the chemicalinteraction between the photocathode 2 and the fiber-optic end wall 12or 120.

I discovered that the contact of the end face 12 or 120 with thephotocathode 2 of alkali-antimony type caused an unexpecteddeterioration of said photocathode. I believe that this effect is due tothe presence of boric oxide or lead oxide which are common ingredientsin glasses which have a high refraction index. It was found that thebest way to prevent this poisoning of the photoemissive photocathode wasto provide a thin light-transparent member 13 between the end wall ofthe tube and the photoemissive layer as shown in FIG. 3. Thelight-transparent separating layer 13 may be of A1 fluorides, MgO orsilicon oxide and it may be of the thickness of a few millimicrons. Itis important that layer 13 of A1 0 or other layer used should be ofcontinuous, nonporous type to prevent exchange of ions through saidlayer. Also same results may be obtained by suing a conductinglight-transparent layer such as or iridium, palladium, or tungsten ofsimilar thickness. In some cases for the best results we may use acombination of a dielectric layer 13 such as of M 0 layer with alight-transparent conducting layer.

I also found that the end face 12 or 120 must be very smooth to preventnonuniformity of the photoemissive layer or of photoconductive layerwhich are deposited thereon. Otherwise false potential gradients will beproduced which will effect the definition of the image.

Another important feature of the construction of my device is theprovision for protecting the vacuum of the tubes 1A or 1C.

It was also found that the caesium of the photocathode 2 causesdiscoloration of the fiber-optic plates 12 or 12a, especially if theycontain lead. The protecting layer 13 will prevent this complication.

The fibers of the fiber plates 12 or 12a when subject to the ionizingradiations, were found to discolor which caused losses of transmittedlight. The addition of cerium to the glass used for making fibersprevented this complication.

As the fibers have a high index of refraction and alkali-antimonyphotocathode has a still higher index of refraction it is advisable tointerpose between the end face 12 or 12a and the photocathode 2 alight-transparent layer of the thickness of the order of odd number ofquarters of wavelength of the light conducted by such fibers and havingan index of refraction n= wanljsth n ra cn.c be sa d n; stile index ofrefraction of alkali-antimony photocathode. This layer 13a may alsoserve as a protecting layer 13 if it is nonporous.

Another embodiment of the divide for intensification of images, is shownin FIG. 6. Two or more vacuum tubes 1, 1A

or 1B and 1C provided with fiber-optic end walls are brought intoapposition to each other and are cemented together. The luminescentimage from the screen 8 is transferred by the fiber-optic end wall 12Aand 12 to the photocathode 2 of the next tube without a marked loss ofresolution.

A modification of this construction is shown in FIG. 6a. Two vacuumtubes IA are connected by means of a bundle of fibers 18 attached to theend walls 12A and 12. The bundle of coated fibers which were describedabove serves to conduct images by internal reflection of light. Thebundle 1 8 may be flexible or may be rigid. The bundle 18 may beattached to the end walls 12 and 12A by an mechanical means or may beseparated from the end walls of the tube. In the latter case, an opticalsystem must be interposed between the end faces of he bundle and the endwalls of the tube.

Another embodiment of my invention is shown in FIG. 7. The tube 21 isprovided with composite screens or intensifying snadwiches" 22, whichcomprise the following layers; a lightreflecting reflectingelectron-transparent layer 23, such as of aluminum or titanium, aluminescent layer 24 such as of zinc cadmium sulfide or zinc silversulfide, a light-transparent separating layer 25 which may e of mica,glass, a suitable plastic such as silicone, or polyester, alone or incombination with a layer of aluminum oxide, silicon monoxide or othersilicon compounds and of the photoemissive layer 26 which may be of anymaterials described above for the photoemissive layer 2. These compositescreens are described in detail in my U.S. Pats. Nos. 2,555,423,2,593,925 and 2,690,516. The intensifying screens are deposited on theend faces of the guide 5. They may be also mounted in apposition to theend face of the guide 5 and will then form a separate unit. In such acase, they will be supported by the light-transparent separating layer,which in this modification will be of glass or mica or of a mesh screencovered with a plastic and A1,O or SiO. It should be understood that theintensifying screen 22 may be also mounted in separation form the endfaces of the guide 5. In such a case, the distance of separation will begoverned by the same rules as described above.

In case the screen 22 is deposited on the end face of the guide, theseparating light-transparent layer 25 may be preferably of silicone orpolyester in combination with a thin layer of aluminum oxide, magnesiumoxide or silicon monoxide or other silicon compounds.

The contact of the photoemissive later 26 with the end face of the guide5 may cause chemical poisoning of the layer 26 and discoloration of theglass. In such case the perforated layer of materials described abovefor the protecting layer 13 must be interposed between the layer 26 andthe end face of the guide 5. The perforated protecting layer 13 must bemounted in such a manner that its apertures will coincide with theapertures 42.

The photoelectrons from the photocathode 2 impinging on the compositescreen 22 will give 10-20 more of new photoelectrons according to theaccelerating voltage used.

It should be understood that a few guides 5 provided with theintensifying screens 22 may be mounted in the same tube for a cascadeintensification of images. It should be understood that the rest of theoperation of the vacuum tube 21 is the same as was described above.

A modification of the invention is shown in FIG. 8. In thisconstruction, the composite screen 22 is disposed between two guides 5.The composite screen 22 may be separated from the end face of the guide5 in which case, the light-transparent separation layer 25 of glass ormica or of a mesh screen covered by a plastic and A1,0, or SiO willserve as a support. The composite screen 22 may be brought in contactwith the end faces of one or both guides S. The composite screen 22 maybe deposited on the end face of guides 5 as one unit. It is an importantfeature of my invention that some layers of the composite screen 22, maybe deposited on the end face of one guide 5 and other layers of screen22, may be deposited on the end face of the next guide, and then bothguides may be brought into apposition together. A good combination is todeposit the layers 23, 2d and 25 on one guide and the layer as on theend face of the other guide 5. Many variations of such splitting of thecomposite screen 22, are feasible and it should be understood that allof them come into the scope of my invention.

It should be also understood that secondary electron-emissive layers 200can be used in combination with the composite screens 22 as shown inFIG. a.

It should be also understood that composite screens 22 may be used onboth sides of each guide 5, either in apposition or in deposition or inseparation from said guide as it was described above.

If the screen 22 is brought into apposition with the guide 5 or if thephotoemissivelayer 26 is in contact with the end face of the guide 5 itis important to prevent chemical interaction between the photoemissivematerial and the materials present in the end face of the guide 5. Thiscon be accomplished by the depositing on the solid parts 44 of the endface of the guide a very thin protecting layer of a plastic, such assilicone or a polyester, or of a glass such as lime glass orborosilicate glass or aluminum oxide or silicon oxide, or a fluoride ora com bination of a few of these materials in the form of superimposedlayers of aforesaid materials. These protecting layers ll3b should bepreferably apertured and deposited so as not to obstruct the apertures4l2 of the guide. The conducting perforated member 7a or 43 may bedeposited on either side of the protecting layers and will be connectedto an external source of electrical potential.

It should be understood that the guide 5 may be sliced into manyseparate segments, and the screens 22 may be interposed between thesegments of the guide. Next all these parts may be combined in one unit,either mechanically or chemically or by heating. This construction willprovide cascade intensification of the images. The protection of thephotoemissive layer 26 from interaction with the materials of the endface of the guide 5 will be the same ab was described above.

It should be understood the composite screens 22 may be used incombination with all types of the electron guide described in thisspecification and may serve in all types of vacuum tubes.

In case the intensifying screen 22 is not supported by the guide 5, theconstruction described above, may be preferably modified in the wayshown in FIG. 9 and FIG. 10. The supporting layer 25 in thisconstruction is replaced by a short bundle of light-conducting fibers 27which were described above. Each fiber comprises a core of transparentglass or plastic 27a of a material, having a high index of refractionthan said core 27b of a'material having a lower index of refraction thansaid core 271: seen as of a glass or plastic and of a metal such asaluminum. The coating 27b is light-opaque to prevent the escape of lightand loss of contrast as was explained above. Sometimes an additionallayer 270 of a light-opaque metal such as of aluminum is deposited onlayer 27b or a metal such as Al or Cr is diffused into the coating 27b.All fibers are fused together at their end only or along their entirelength by heating them or by gluing them into one unit. The other layersof the composite screen such as layers 23, 24 and 26 are mounted on therespective end faces of the fiber bundle 27. This construction offers amuch greater ruggedness than the previously described screens 22 andwithout loss of resolution.

The photoemissive layer 26 has to be protected from the interaction withthe materials in the bundle of fibers 27 in the same way as wasexplained above, by layer 13.

Another way to make the composite screen 22 rugged without sacrificingresolution or contrast of images is shown in FIG. a. In thisconstruction, the supporting layer of the screen 22, is replaced by awide-mesh screen 2% which is coated on each side or on one side onlywith a layer of silicone 28a or of polyester or of otherlight-transparent heat-resistant, low-vapor plastic. On one side, of thelayer 28a, there is deposited in addition, a light-transparent, verythin layer of aluminum oxide, magnesium oxide or silicon oxide or othersilicon compounds. It should be understood that the construclid tion ofthe composite screen 22 described in FIG. ill) or Illa applies to allembodiments of my invention in which such a screen is used.

Another great advantage of my invention resides in the pos sibility ofpreparing the luminescent screen fl and the photoemissive layer 2 in aclose spacing to each other, without the danger of contamination of theluminescent material of the screen b3 by caesium or other vapors whichhas not been possible in the prior art. In my device, the photoemissivelayer 2 and screen ii are separated by the guide 5 which prevents thespreading of Cs to the screen b. If a perforated type of layer 7 isused, the apertures of channels 6 may be closed by a layer ofnitrocellulose or of other material which will be removed by the bakingprocessing of the vacuum tube.

When a plurality of guides 5 with intensifying screens 22 or 7a-20a areused, it may be advantageous to process the guide 5 with the screensattached to it outside of the vacuum tube in a demountable extension ofsaid tube. After completion the guide 5 with the screens 22 isintroduced into the final vacuum tube and is mounted there by mechanicalmeans.

The sensitivity of my imaging devices described above may be furtherincreased by using a novel optical objective for focusing the image onthe photocathode 2 which is a combination of a lens 311 with a taperedlight conducting fiber bundle 32, instead of using the lens alone, asshown in FIG. 111. The fiber bundle 32 may be attached to thefiber-optic end wall 12 of the vacuum tubes carrying the photocathode 2,which were described above, by any mechanical means. The fiber bundle 32comprises a plurality of tapered fibers 27d for the demagnifying of theimage produced by the lens.

Each fiber comprises a core of transparent glass or plastic 27a of amaterial, having a high index of refraction and a coating 27b and of alower index of refraction than said core 27a of materials such as of aglass or plastic and of a metal such as aluminum. In some cases it ispreferable to use glass or ceramics which will tolerate a hightemperature such as at least 6000 C. In some cases the coating 27b ispreferably light opaque to prevent the escape of light and loss ofcontrast, or an additional layer 27c of a light-opaque metal such as ofaluminum is deposited on the layer 27b or a metal such as AC or Cr isdiffused into the coating 27b to :render it light opaque as wasdescribed above. All fibers are fixed together at their ends only oralong their entire length by heating them or by gluing them chemicallyinto one unit. If the fiber bundle should be flexible, then only theends of the bundle should be fixed together. If a rigid bundle iswanted, then the fibers are fixed together along their entire length.

In modification of this invention, the fiber bundle 32 may enter thevacuum tube 1F and form a part of its end wall which in this case, doesnot have to be made of fiber-optic plate, but may be of the usual glassor metal, construction. The fiber bundle 32 will therefore form a partof the end wall of the tube or it may replace the whole end wall. Thephotocathode 2 is then deposited on the end face of the bundle 32. At itwas described above, precautions must be taken to prevent chemicalinteraction between the fibers of the bundle and the photoemissive layer2. A very thin light-transparent separating layer 13 should therefore beinterposed between the end face of the bundle 32 and the photoemissivelayer 2. The layer 13 may be of aluminum oxide, magnesium oxide or othersilicon compounds.

Another modification of my invention which is shown in FIG. 23 will beof a great importance for television pickup tubes which have'an imagesection such as image orthicon or image vidicon. My device will permitelimination or electrostatic or electromagnetic focusing devices in theimage section used in the present television tubes. In thisconstruction, the photoelectrons from the photocathode 2 of the imageorthicon, or other television pickup tube, are guided to the target 36)by the guide 5. The electrons transmitted through the guide reach thetarget 3% which is closely spaced to said guide without loss ofresolution.

It was also found that the perforated mesh screen used to collectsecondary electrons degrades resolution in television camera tubes. Inmy invention it may be replaced by a continuous conducting layer 7 whichis mounted on or adjacent to the end face of the guide close to thetarget 30 instead of a mesh screen. The electrons from the photocathode2 focused by the guide 5 have velocity high enough to pass though thelayer 7 which is made very thin to be transparent to electrons, and toimpinge on target 30. The secondary electrons from the target 30 arecollected by the layer 7.

My invention can be also used for images of invisible radiations such asX-rays infrared, or images of atomic particles such as neutrons orelectrons or for images formed by supersonic waves. In such case, thephotocathode 2 must be modified, to make it responsive to the radiationused for image-forming purposes. The photocathode for X-rays or atomicimages were described in my US. Pats. Nos. 2,555,423 and 2,690,5l6. Thephotocathodes described in the above patents, may be modified by using afiber-optic bundle 27 instead of a light-transparent separating layer,as it is shown in FIG. 9, or by a screen shown in FIG. a.

The photocathode for supersonic images will comprise a piezoelectricplate 35 covered by a continuous or mosaic layer 34 of a photoemissivematerial such as was described above for the layer 2, as shown in FIG.130. The layer 34 is irradiated uniformly by a source of light 65causing emission of a beam of photoelectrons. The supersonic image isconverted by piezoelectric layer 35 into a pattern of potentialscorresponding to said image. This voltaic or charge pattern modulatesthe emission of photoelectrons from the layer 34 or of secondaryelectrons from the layer 36. The photoelectron beam has therefore thepattern of the original supersonic image. The photoelectron beam entersthe guide 5 and remains focused by said guide. It may be alsointensified if the guide has secondary electron-emissive layer a or 20or screen 22, as was described above. The intensified electron beam maybe converted into a visible image as was explained above illustrated inFIG. 1 or it may be converted into video signals as it was illustratedin FIG. 13.

In other modification 68 shown in FIG. 130 the piezoelectric plate 35 iscovered by a layer of a secondary electronemissive material 36 of one ofmaterials described above for the layer 20 or 20a. The electron guide 5in this modification has a hollow tunnel 37 through which the electronbeam from the electron gun 40 may pass and impinge on layer 36 in ascanning pattern to produce a secondary electron emission from it. Thedeflecting means 53 will serve to produce a scanning motion of theelectron beam. The high velocity electron beam from the electron gun 40causes secondary electron emission from the layer 36. This electronemission is modulated by the voltaic pattern in the pate 35. Thesecondary electrons enter the guide 5 and are intensified there bysecondaryelectron emission, as it was described above and shown in FIG.le or FIG. 4. The multiplied electrons may be converted into videosignals, as it is known in the television art.

It was found that the device 67 shown in FIG. 13c failed when a standardsource of light was used. It was found that devices 67 or 69 couldoperate well only if the source 65 emitted only red or infrared light.In addition the source of light 65 should be preferably monochromatic orshould emit in a narrow range of wavelengths. The use of standard sourceof light causes emission of photoelectrons ranging from 0.1- volt to5-volts velocity. It was found that such range of photoelectrons couldnot be modulated with piezoelectric voltages on the plate 35.

The piezoelectric layer 35 may be of a continuous type or of adiscontinuous mosaic type in all devices described.

The supersonic image devices shown in FIG. 13a, 13b, and 13c may befurther improved by combining the piezoelectric layer 35 with a member70 which intensifies supersonic waves. The member 70 may be in the formof a thin layer of a semiconducting material such as CdS or ZnO.Especially CdS of a thickness of a few microns exhibits strongamplification of supersonic waves. Addition of activators such as Cueither by diffusion of Cu into CdS or by evaporation of Cu with CdSincreases this amplification effect further. The amplifying layer 70should be plated with conducting layers 72 and 73 such as of indium ortin oxide which are connected to a source of electrical potential toprovide a uniform field through said layer 70. The conducting layer 72preferably should be light transparent. It was found that irradiation oflayer 70 with light through the conducting layer 72 improves supersonicamplification. The supersonic amplifying layer 70 is responsive tolongitudinal and to transverse supersonic waves and responds to a verywide range of frequencies of supersonic waves. The intensifiedsupersonic waves emitted by layer 70 impinge on the piezoelectric layer35 through the conducting layer 73 and produce potential or chargepattern corresponding to the original supersonic image.

In a modification of my invention the supersonic amplifying layer 70 ismade preferably in the form of a mosaic 71 formed by a plurality ofislands of CdS, ZnO or other suitable material and is mounted on thepiezoelectric plate 35 as shown in FIG. 13a. Such a mosaic may beproduced by evaporating the amplifying material through a mask or a meshscreen on a piezoelectric plate 35 which is first coated with aconducting layer 73. After evaporation of the mosaic 71, electricallyconducting layer 72 is evaporated to provide the second electrode.

The piezoelectric layer 35 may be a self-supporting layer, and may serveas a support for the other layers and may also form the end wall of thevacuum tube.

It was found that difficult bonding problems arise in bonding thepiezoelectric layer 35 to the glass of the envelope of the vacuum tubeto make it the end wall of the tube. The use of indium seal or of epoxyseal is not efficient when piezoelectric plates of a large diameter haveto be cemented, as it is required in some applications. It was foundthat the best solution is to use a vacuum tube envelope of a ceramic.The piezoelectric plates of a large diameter may be well joined to saidceramic envelope by brazing. In some cases the tube envelope of a metalis preferable and it was found that piezoelectric plate 35 of quartzcould be well bonded with the metallic envelope. Another solution ofthis problem is to mount the piezoelectric layer 35 on the insidesurface of the end wall of the vacuum tube.

In some cases the conducting layer 72 or 73 may be eliminated. Thismodification applies to all embodiments of my invention.

The piezoelectric layer 35 may be of a continuous type or of a mosaictype. It may be made of titanates, quartz, niobates or otherpiezoelectric materials. The layer 35 may have a high resistivity suchas 10 ohm-cm., or it may be of a semiconducting material, havingresistance of I0 ohmcm. to I0 ohmcm. titanates niobates can be preparedin a semiconductive form by doping them with suitable agents. The mosaictype of layer 35 may be constructed by assembling a plurality of smallcrystals or by evaporating a polycrystalline layer or bymechanicallygrooving a large crystal into many small units.

Supersonic waves can be conducted by the fiber bundle 27 describedabove. By using as a source of image-forming radiation piezoelectric ormagnetostrictive generators of supersonic waves and conducting saidwaves to the examinedpart,

. we may produce supersonic images. Piezoelectric generators may be inthe form of oscillating crystals of quartz, titanium compounds, such astitanates, Rochelle salts and other similar materials. The supersonicwaves may be directed to the examined part by supersonic lenses orpreferably by means of the fiber bundle 27. The supersonic wavesreflected or transmitted by the examined part may be directed to thesupersonic image-sensitive member by the same fiber bundle or preferablyby an additional fiber bundle. The supersonic-sensitive member may havethe form of piezoelectric elements, such as were described above for thesupersonic generator, but smaller in size. In another embodiment ofinvention, the supersonic image-sensitive members is a vacuum tubeprovided with a piezoelectric continuous or mosaic electrode 35; saidpiezoelectric screen or electrode receives the supersonic image of theexamined part and converts said image into an electrical pattern ofpotentials or charges which correspond to said supersonic image. Such avacuum tube is provided with a source of electron beam, such as electrongun for irradiation of said piezoelectric screen or electrode. Theelectron beam scans said piezoelectric screen or target is modulated bythe electrical pattern present on said screen or electrode and thereturning modulated electron beam is converted into electrical signalsin the manner well known in the television art.

In some cases the photoemissive layer 34 or secondary electron-emissivelayer 36 may be mounted in a closed Spacing to the piezoelectric layer35 as a separate unit. In such case the layer 34 or 36 must have aperforated support such as member 43 described above. The support forthe layer 36 should be preferably of conducting material but in somecases dielectric material may be also used. The unit 43-36 or the unit43-34 may be in contact with the layer 35 or may be mounted at a verysmall distance from the layer 35 such as one or a few microns at most.The electrons emitted by the layer 34 or 36 will enter the novel guidefor their focusing and in some cases for their further intensificationas was described above.

In another modification 69 of this invention the photoemissive layer 34or secondary electron-emissive layer 36 are mounted on the end face ofthe electron guide 5. The electron guide 5 is mounted in a distance of 1or a few microns from the target 35, as shown in FIG. 13b.

My device will be useful for construction of a novel electron gun whichwill offer an improvement of resolution of the electron beam. It is wellknown in the art that it is difficult to produce an electron bema of asmall diameter without use of strong electrical or electromagneticfields. My electron guide 5 and its modifications will permit theproducing of the electron beam as small as of lO-microns diameter orless without focusing fields. This construction is shown in FIG. 14. Theelectron beam emerging from the source of electrons 40 enters into aclosely spaced guide 5 having the apertures 42 of the size of 5 tomicrons, or of any other size desired and which is mounted in the vacuumtube llD.

The guide 5 has essentially the same construction as was described aboveand all modifications of the guide 5 apply for the use in the novelelectron-gun 62 construction. In case a scanning electron beam is wantedthe deflecting members 53 will direct the electron beam sequentiallyinto various apertures 42 of the guide 5 to produce a scanning pattern.The deflecting means may also be mounted after the guide 5 instead of infront of it and will deflect the electrons after they were transmittedthrough the guide 5. The electrons traveling through the tunnels 6 ofthe guide remain focused therein. As the electron beam emerges from theapertures on the exit side of the guide 5 or 5A it has the same spotsize it had at its entrance into the guide. It should be understood thatthe guide 5A may have tapered tunnels as it was described above, whichmay be of convergent form, in which case the electron beam will bedemagnified upon its exit. In other cases, the tunnels may be ofdivergent form in which case the electron beam will be magnified uponits exit. It should be understood that apertures 42 may have a bevelledshape or other shapes.

The problem of prevention of space charge development will be solved inthe same way as was described above.

In order to obtain the best definition of the electron beam theelectrons which travel through the tunnels 6 of the guide 5A must beprevented from striking the walls of said tunnels. This can beaccomplished by providing the walls of said tunnels which face the lumenwith a conducting or semiconducting coating 7a. The conducting coatingmay be of aluminum or chromium. The semiconducting coating may be of tinoxide or of titanium oxide. The coating 7a may be connected to theperforated conducting member 43 or 7b which again maybe connected to anoutside source of an electrical potential. As all tunnels s are incontact with the member 43, walls of said tunnels will have anelectrical potential which will repel electrons. In this modificationthe tunnels 6 should be normal to the electron beam and the apertures 42symmetrical in shape.

In some cases, the second perforated member 43 is mounted on theopposite end of the guide 5 or 5A. In this construction the member 43amay be connected to the external source of potential to provideacceleration for electrons.

In addition my electron gun can bring about intensification of theelectron beam produced by the electron gun 40 without increasing thenoise of the electron beam, which is of the utmost importance for manydevices. The intensification of the electron beam from source 40 such asstandard electron or matrix gun may be accomplished by all constructionsdescribed above, for example by depositing a very thin secondaryelectron-emissive layer 200 on the end face of the guide 5A as wasdescribed above and illustrated in FIG. 5. The electron-emissive layer20a is deposited on the end face of the guide. On layer 20a is mountedelectrically conducting layer 7 or 7a or 43 thin as to be transparent toelectrons, and connected to a suitable source of potential. The layer20a may be continuous, but preferably it should be discontinuous. In thediscontinuous construction it may overlie the apertures 42 of tunnels dbut be absent from the solid parts of the guide 5 except around theedges of apertures. In some cases the electrically conducting layer 7bwhich provides potential for the secondary electron emissive layer 20ais deposited not only over the apertures of the guide 5, but as acontinuous layer 7 extending over the solid parts of the end face of theguide and over the apertures of the guide as well. This constructionwill be important for prevention of the accumulation of the space chargewhich may be very detrimental for the operation of the novel electrongun 62.

If the secondary electron-emissive layer 200 is used on the end face ofsecondary guide 5, it is preferable to deposit first said layer 20awhether it be in the form of a continuous layer or in the form of adiscontinuous layer on the end face of the guide and then to mount themember 43 or 7, as shown in FIG. 5 or FIG. 14. In some cases thesequence of the layer 200 and of the member 43 may be reversed and themember 43 is the first one to be mounted on the end face of the guide.It should be understood that in cases in which the fragility of thisdevice is not very critical the layer 20a and the member 43 may bemounted as one unit spaced apart from the end face of the guide 5 or 5A.They must be however very closely spaced in relation to said end face sothat the secondary electrons will enter the apertures 42 without causingloss of resolution.

Further intensification of the electron beam may be accomplished byusing a few guides 5, 5A or 5D each of them being provided with asecondary electron-emissive screen comprising layers 43 and 20a. Allsuch guides are combined in one unit by mechanical means, chemicalmeans, or by heating. In this way a cascade intensification will beobtained. It should be understood that all modifications of the guide 5may be used for such a cascade or tandem construction.

An additional intensification of the electron beam from the electron gunmay be accomplished by depositing the secondary electron-emissive layer20 on the inside walls of the tunnels 6a, as it was explained above. Theelectron beam from the electron gun in such case is directed intoapertures of the guide not normally but at an angle, the size of whichwill depend on the spacing between the electron gun 40 and the size ofapertures 42. The oblique entrance of the electron beam into tunnels 6acauses impingement of the electrons on walls of the tunnels 6 andproduces thereby secondary electron emission from the layer 20. Thematerials for the layer 20 were described above. The layer 20 isdeposited on the electrically conducting layer or semiconducting layeror resistive layer 70 as it was explained above, and which is connectedto the source of electrical potential. The secondary electrons emittedfrom the layer 20 strike the next part of the wall of the tunnels 6a. Inthis way, the intensification process is repeated until the electronsemerge from the tunnels 60. As the electrons emerge from the guide, theelectron beam size remains limited to the size of the diameter of theaperture, but it is greatly intensified, without introduction of anyadditional noise.

It should be understood that my device will be useful for all sources ofelectron beams whether the electron beam is produced by a hot filamentor by a cold emission or by a field emission. It should be understoodtherefore, that the definition electron gun" used in this specificationand in the claims embraces all such sources of the electron beam.

It should be also understood that all modifications of the electronguide such as 5A, 5B, 5C or 5D described above may be used for theconstruction of the novel electron gun".

It should be understood that this novel electron gun may be used fortelevision camera tubes, for kinescopes, for black an white images orfor color images, and for storage tubes. It should also be understoodthat my device will be useful for devices using a broad electron beamsuch as applied for reading" in storage tubes or for electron mirrortubes.

My invention will be of great importance for construction of novelstorage tubes such as having electron gun or a photocathode or both. Thepresent storage tube has a very low resolution such as ,5 pair lines permillimeter. I found that this low resolution is due to inability of thestorage target in these tubes to focus the broad reading electron beaminto a plurality of electron microbeams small enough to depict imagepoints of a minute size such as it is necessary e.g. for resolution ofpair lines per millimeter.

This problem was solved in my device in which the broad electron beam issplit into plurality of small electron beams by the novel electronguide. The split electron beam can be as small as 10 microns in diameterand will give the final image of a high resolution which was notpossible before.

In conclusion my invention allows the separation of the two functionswhich were before provided by the storage target of the prior art, suchas modulation of the broad electron beam with'a stored charge patternand focusing of said beam.

In this embodiment of invention, shown in FIG. the electron guide 5B inthe vacuum tube 1E has the electrically con ducting member 43 or 7b ofaluminum or nickel such as was described above, deposited on the endface of the guide 58. Next the secondary electron emissive layer 52 ofdielectric material such as alkali halides or MgO or AL O is depositedon said conducting member 43.

The sequence of the layer 52 and of the member 43 may be reversed insome cases and the layer 52 is deposited on the end face of the guide 58first.

The member 43 and layer 52 are deposited on the solid parts 44 of theend face of the guide 58 in such a manner as not to obstruct theapertures 42.

In operation of this storage device, the photoelectrons from thephotocathode 2 or from another source of electron beam which is imagemodulated such as an electron gun 40 are directed to the end face of theguide 58 and impinge on the secondary electron-emissive layer 52producing a positive or negative charge image on the end face of saidguide according to the potentials used. The charge image cannot leadaway because it is formed on a dielectric layer 52 as shown in FIG. 15.As a result a stored charge image remains on the end face of the guide58 and has the pattern of the original electron image. Next a broadnonmodulated electron beam is produced either by irradiation of thephotocathode 2 with a uniform source of red or infrared light, or byusing an electron gun 40 for this purpose. The broad electron beam as itenters the apertures 42 of the guide 53 will be modulated by the storedcharge image, and will have, therefore, imprinted on it the pattern ofthe original image. The broad electron beam is decelerated before theend face of the guide by a mesh screen or by conducting rings connectedto a suitable source of electrical potential. The broad electron beamsafter being split into plurality of microbeams by the electron guide 58is directed onto image-reproducing screen and reproduces a visibleimage. Instead of a luminescent screen 8 other types of screens such asscotophore screens, targets, such as dielectric tape, or photoconductiveor semiconductive targets may be used as well.

It should be understood'that the storage unit 43-52 may be mounted inapposition or in a close spacing to the end face of the guide 58 as aseparate unit.

It should be understood that the electron guide 58 used in thisembodiment of the invention may be made by any method and may be of anytype described in this specification. It should be understood thereforethat reading electron beam may be intensified by secondary electronmultiplication and by cascade use of plurality of electron guides.

In some cases, instead of a storage material 52 0f a dielectric type, asemiconducting material or even a conducting material such as Be, Cu, orNi may be used. Such conducting storage layer must be deposited as adiscontinuous mosaic on the dielectric solid parts 44 of the end face ofthe guide 53 and will be able to store the charge pattern because of itsdielectric base.

It should be understood that the electron storage-guide unit may be alsoused in any type of vacuum tubes such as camera television tubes,kinescopes etc. and my invention is not limited to the image type oftube 1E.

It should be understood that all vacuum tubes described above may beoperated in a continuous manner, or is a pulsed manner. In the pulsedoperation the potential for the acceleration of electrons from thephotocathode 2 or electron gun 40 is suspended for a short duration.This time interval may be also used for providing a suitable positive ornegative potential to the conducting or semiconducting coating on theinside walls of tunnels 6 in order to eliminate positive or negativespace charge accumulations. The positive potential may be applied to theend face of the guides 5 to dissipate the negative charges presentthereon, or a negative potential may be applied to dissipate positivecharges present thereon. It will depend on the type of the vacuum tubeand on its operational voltages whether we will have positive ornegative space charge. I

It should be understood that all types of the electron guide may be usedin each embodiment or modification of my invention.

It should be understood that the word glass" in claims embraces all kindof glasses and of plastic materials as well.

It should be understood that the word light" in claims embraces allvisible and invisible radiations.

It should be understood that word tunnels in his specification and inthe appended claims means passages which have walls completelysurrounding said passages leaving only the end faces open. It is incontradistinction to channels which are not surrounded by walls on allsides.

As various possible embodiments might be made of the above invention,and as various changes might be made in the embodiment above set forthor shown in the accompanying drawings is to be interpreted asillustrative and not in a limiting sense.

It should be understood that all types of the electron guide may be usedin each embodiment or modification of my invention.

A great improvement of definition and contrast of images was realized inthe embodiments of invention shown in FIG. 15c, 15a, and 15b. In thisconstruction the tunnels 81 of electron guide and multiplier are curved.Without going into theoretical explanation it is sufficient to say thatthe construction of the electron guide device built of strongly curvedor even spiral tunnels in contradistinction to the straight tunnelsmarkedly improved the performance of all my devices both in definitionand contrast of images and instability of operation.

It was unexpectedly found that the image will be faithfully reproducedregardless of the curvature or in tortuosity of the tunnels 81 as longas the spacial relationship of all entrance and exit apertures remainsthe same. It was also found that apertures of entrance into tunnels 6,80 or 83 and apertures for exit from said tunnels do not have to becoaxial. It means that apertures for exit of electrons maybe in adifferent plane than the entrance apertures and in spite of it the imagewill be faithfully reproduced, as long as the spatial relationship ofall exit apertures is the same as the spatial relationship of allentrance apertures.

Another important finding was that the tunnels 81 between theirapertures blla and Mb may be of different diameter and shape than theapertures themselves without affecting the definition of the images. Itwas found that the definition of images depends only on the dimensionsof apertures and how closely said apertures are spaced to each other andnot on the dimensions of tunnels between said apertures.

It was further found that the diameter of the tunnels may vary withincertain limits along their length without affecting the resolution ofimages. It was also found that the tunnels may be separated along theircourse from each other and that the definition of images will not sufferas long as the entrance apertures and the exit apertures of tunnels Mare spaced as closely to each other as it is possible.

In view of the above findings the curved construction of the electronguide MI was found to be feasible and compatible with a good definitionof images. It should be understood that the curved or spiralconstruction of the electron guide and multiplier b applies to allmodifications of my electron guide or multiplier and that it may be usedin all devices described herein. The curved construction of the electronguide 80 created a new problem The electron guide 80 uses 100 to 500tunnels in each plane, as each tunnel represents one image point. Inorder to bring this number of curved tubes or other hollow members whichform tunnels in apposition together, each successive curved tube must bea little longer then the preceding one. As a result the 100th tube willbe considerably longer than the first tube, if the apertures of alltubes in all planes of the electron multiplier 80 should be in one andthe same vertical plane, as it is shown in all FIGS. I to I14. It wasfound however that the great differences in length of tunnels BI cannotbe tolerated because they cause great differences in output signalsproducing thereby incorrect contrast values. The solution of thisproblem is to equalize the length of all tunnels as shown in FIGS. 115aand b. It should be understood that in devices in which the contrast isnot important the equalization of length of tunnels may be omitted. Theconstruction based on equalizing the length of all tunnels results information of end face d2 of the electron guide 80 which has slantedshape, which means that it is inclined at an angle to the long axis ofvacuum the tube, as it is shown in FIG. 15a. In some cases it may bepreferable to equalize the length on both entrance and exit side of theelectron guide fill as it is shown in FIG. 15b. The slanted end face 82of the electron guide was found to cause geometrical distortion ofreproduced images if conventional focusing means were used. Thisdistortion can be improved by using suitable electron-optical lenses. Itwas found however that a simple solution was to mount theimagereproducing screen such as a luminescent screen 8-9 or a target ofthe television tube also at an angle so that the end face 82 andimage-reproducing screen are parallel to each other, as shown in FIG.I511.

If the image-reproducing screen is the target of a television pickuptube, the scanning electron tube when scanning such slanted targets willcause so-called trapezoidal distortion of the image. Suitable-focusingelectron-optical lenses to correct such distortion are known in the artand do not have to be described in detail.

Another modification of curved electron guide and multiplier 80 is aspiral electron multiplier $3. The electron multiplier 83 is constructedof spiral tunnels @311.

The spiral construction of tunnels is shown in FIG. ll5c. It was foundto be compatible with resolution of images provided the entranceaperture @Ia and exit apertures bllb are spaced in contact or in aclosed apposition to each other. The spiral construction requireshowever a large size vacuum tube as an array of spiral tunnels 83aoccupies a much larger space than array of curved-typed tunnels M. Theequalization of the length of all tunnels is necessary also in thismodification of the invention and was described above.

It should be understood that the spiral electron multiplier b3 may haveall modifications of electron guide and multipliers described inspecification and may be used in all devices described herein.

It should be understoodm image-intensifying devices described in thisspecification whether they are of image-tube type or television type orof storage-tube type may be modified to make them responsible toinvisible radiations of electromagnetic type such as X-ray ultravioletor infrared, or of atomic-particles type such as neutrons or protons, orof acoustic type such as supersonic radiation.

FIG. I6 shows the X-ray-sensitive image intensifier 85. Instead of aIight-sensitive photocathode 2 I am using a composite photocathode in aform of a screen which comprises a fluorescent or luminescent layer 2dand a photoemissive layer 26. Such screens were described above. Torhigher energy X- rays such as gamma rays a photocathode of gold or leadmay be used alone or in combination and in apposition with the compositescreen 22 described above. In some applications the fluorescent layermay be mounted on the outside surface of the end wall of the vacuumtube, the photoemissive layer 26 being mounted inside of the vacuumtube. The X-ray imageintensifier converts the X-ray image into afluorescent image. The fluorescent image is next converted into aphotoelectron beam corresponding to said image. The photoelectron beamis fed into the electron multiplier 5 or modifications, or 33. Themultiplied electron beam exiting from the multiplier 80 is projected orfocused on the image-reproducing screen such as luminescent screen e.g.Ii-b or on a target of a television pickup tube such as 30 or on astorage unit such as 4l0-52. It was found that the electron multiplierM) or $3 is very useful for intensification of X-ray images. It wasfound that besides the intensification of the photoelectron beam emittedfrom the composite photocathode 22, it provides also a directutilization of the X-ray beam which carries the X-ray image. Inparticular it was found that only 15 percent of the X-ray beam isabsorbed in the composite photocathode 22. The rest of the X-ray beampasses through said photocathode and strikes the input end face of theelectron guide Ml or 83. The impinge ment of the X-ray beam on thesecondary eIectron-emissive coating of material on the inside surface ofthe lumen of the tunnels M or 83a results in conversion of X-ray photonsinto electrons. The emitted electrons are now multiplied in the electronguide 5, M) or 33 as we described above. In order to prevent the loss ofdefinition we must prevent separate fine pencils of the X-ray beam whichcorrespond to separate image points from striking a few tunnels ofelectron guide instead of being limited to essentially one tunnel only.In addition it was found that the electron multiplier should be spacedin the vacuum tube in a symmetrical position in relationship to thesidewalls of the tube which means that it should be at the same distancefrom both sidewalls.

In some cases but not for X-ray applications, it is necessary to provideelectron-optical demagnifying means either of electrostatic orelectromagnetic type between the composite photocathode 22 and theelectron guide or multiplier 5, till or 83. This arrangement will permitthe use of an electron multiplier smaller than the photocathode which isimportant in some applications. In addition it will provide an extraintensification of the image.

In other applications it was necessary to use electron-optical means ofmagnifying type in order to enlarge the image from the photocathodebefore projecting it on electron guide or multiplier. This arrangementwill permit to preserve the definition of images which is available inthe photocathode and which is too high for electron guide or multiplierto reproduce. For example the photocathode may be able to produce animage having definition of IS pair lines per millimeter. On the otherhand a particular electron multiplier for example can produce images ofonly 5 pair lines per millimeter definition. By using electron-opticalmagnification by a factor of 3, the image on the end face of theelectron multiplier will now have definition instead of 15 only of 5lines per millimeter and will be therefore resolved well by the electronmultiplier. After the passage through the electron multiplier the imagemay be again demagnified if necessary and the original definitionregained.

In X-ray applications the electron-optical 82a magnifying ordemagnifying means can be used only if mounted between the electronmultiplier and the screen for receiving electrons exited from theelectron multiplier, such as fluorescent screen 8 or a target televisiontube 30, which is shown in FIG. 20.

It should be understood that the use of the electron-optical 82a meansdemagnifying or magnifying means applies to X- ray devices and to allother embodiments of the invention.

FIG. 17 shows the neutron-sensitive image intensifier 85a, wherein aneutron reactive layer 86 preferably from the group boron, lithium,gadolinium and uranium or of paraffine is placed on the face of theimage tube. The protons or electrons liberated from this layer 86 underthe impact of neutron radiation will strike directly or through a thinelectron-pervious chemically inactive barrier layer, a suitablefluorescent layer 24, causing it to fluoresce and activate a suitablephotoemissive layer 26 through the light-transparent barrier layer 25.In other cases a neutron reactive layer of copper or other gamma emittersuch as cadmium 88 will be more advantageous, because of its gammaemission and may be mounted on the outside surface of the end wall 87 ofvacuum tube or may be adjacent to said end wall but spaced apart fromsaid wall 87, as it is shown in FIG. 18a.

In some cases it may be more desirable to eliminate the fluorescentlayer 24 and to cause protons and electrons from the layer 86 to act onelectron-emissive layer either by apposition or by focusing them withmagnetic or electrostatic fields. In some cases the electron-emissivelayer may be omitted and the beam of the atomic particles from theneutron reactive layer 86 may be focused directly on the electron guideand multiplier or its modifications, 80 or 83.

The fluorescent layer 24 may be also combined with the layer 86 or 88 inone composite layer and may be in this form mounted within the tube oroutside of the tube 85a.

The fluorescent layer to be used in the neutron-sensitive tube may be ofa similar composition as described above in the X-ray-sensitive imagetube 85, but it has also to be adapted to respond most efficiently tothe radiation emitted from neutron-sensitive layer by enriching it withproper additional elements. The photoemissive layer has again to becorrelated with spectral emission of fluoresceht layer. The other partsof the tube 85a are the same for neutron-sensitive image tube and forX-ray sensitive image tube 85.

FIG. 18 shows infrared-sensitive image intensifier 89. Instead of thephotocathode 2 a very thin layer 90 or black gold or platinum is used.The impingement of infrared radiation through a suitable window in theend wall of the vacuum tube 89 such as of sodium chloride, quartz orarsenic sulfide produces in said layer 90 a pattern of differenttemperatures corresponding to the pattern of said infrared image. Theadjacent photoemissive layer 26 is irradiated by light from anextraneous source 91. The emission of photoelectrons in modulated bysaid pattern of temperatures in said layer 90. The emittedphotoelectrons are directed into entrance apertures of the electronguide 5 or its modifications, 80 or 83 for multiplication. The rest ofthe construction of the tube 89 is the same as in any one ofmodifications described herein.

FIG. 18a shows another modification of the infrared-sensitive imageintensifier. In this construction the layer 90 of gold or platinum isfollowed by a layer of photoconductive material 92 such as PbS, PbSe,PbTe or Se.

Next follows a very thin chemically inactive barrier 93 such as of MgO,SiO or SiO, or TiO,. On layer 93 is mounted a very thin conducting layer93a such as of tungsten, platinum or palladium which may be in the'formof a continuous layer of a mosaic layer. In some cases the photoemissivelayer 26 which may be in a form of a continuous layer of a mosaic layer.In some cases the photoemissive layer 26 and conducting layer 93a may bemounted spaced apart from the photoconductive layer 92. In such case thebarrier layer 93 may be omitted. The infrared beam causes changes inelectrical conductivity of layer 92. The layer 92 is connected to oneterminal of a source of electrical power 91a such as battery or to asource of a lowfrequency electrical current? The other terminal of theelectrical source 91a is connected to the conducting apertured member 94mounted after the photoemissive layer 26 and spaced apart from it. Thescreen 94 is biased in such a manner that the photoelectrons from thelayer 26 cannot pass through it in the absence of the infrared imageforming radiation. When he infrared image arrives, it causes a drop ofresistance in the layer 92. This results in the lowering of cutoff biasvoltage in the apertured screen 94. Now the photoelectrons from layer 26can pass through said member 94 and may be fed into electron multiplier5 or its modifications or 83. The multiplied electron image has thepattern of the original infrared image and is now projected or focusedon the image-reproducing screen such as a luminescent screen 9-8 or on atarget of a pickup tube such as 30 or other targets or on a storagetarget.

My invention will allow the construction of a novel electron or othercharged-particles microscope such as proton or ion microscope or thediffraction cameras. One of most vexing problems in the present electronmicroscopy is the damage of the examined specimen by the exposure to theelectron beam. The electron beam causes irreversible changes in thestructure of organic or inorganic objects as well. As a result imagesare obtained and recorded which in reality do not exist at all andrepresent artifacts only. The only way to eliminate or to reduce suchartifacts is to decrease the intensity of the examining electron beam.The reduction of the intensity of the electron beam without prolongingthe exposure time is unfortunately impossible because of the limitedsensitivity of photographic materials used to record theelectron-microscopic image. It is therefore, the objective of thisinvention to eliminate the artifacts by reducing either the strength ofthe electron beam irradiating the examined specimen or the exposure timeor both.

The prevention of feedback of ions which is one of the objectives of thecurved configuration of tunnels 81 and their modifications is possiblealso by other configurations in which the longitudinal axis deviatesfrom the straight line between the input apertures and exit apertures oftunnels. This embodiment is shown in FIG. 19 which illustrates electronmultiplier 80B constructed of two or more electron multipliers A and Bof standard type with straight tunnels. These multipliers A and B havehowever tunnels which run obliquely which means diagonally and haveopposite direction to each other. It means that the multiplier A hastunnels running from above downward whereas the multiplier B has tunnelswhich run from the bottom upward. If multipliers A and B are joinedtogether, so that the exit apertures of multiplier A correspond to theentrance apertures of multiplier B, we will obtain an angulatedlongitudinal axis of tunnels and an angulated path of electrons throughsuch united multiplier 808 which was the objective of this construction.The union of multipliers A and B must provide for the electrical andmechanical continuity of the walls of tunnels belonging to multiplier Aand of tunnels belonging to multiplier B.

It was found that in all configurations of the composite multiplier 808the multiplier B should be much thinner, which means that it should havea much shorter longitudinal axis than the multiplier A. Thisconstruction will bring the point of deviation of the longitudinal axisof tunnels 81d from the straight line to be close to the exit apertures81b and till therefore stop the back-running ions before they canproduce damage. For the best results the ratio of the thickness ofmultiplier A to multiplier B should be not less than 4 to 1. This atrangement will cause however displacement of the relation between theinput apertures 81a and exit apertures 81b. In X ray image intensifierssuch displacement can be tolerated only if not exceeding 1 mm., as itwas explained above. This limitation does not apply to imageintensifiers other radiations than X-rays or neutrons.

Other configurations of angulated tunnels are possible. In particular itwas found advantageous to use a multiplier A or B with oblique tunnelsin combination with a second multiplier C which has straight tunnelssuch as in electron multiplier 5.

This arrangement is illustrated in FIG. 19a which shows multiplier Awith oblique tunnels and multiplier C with straight tunnels unitedtogether. This construction may be reversed in that the multiplier Awill have straight horizontal tunnels 6 and multiplier B will haveoblique tunnels.

The requirement for electrical continuity and for mechanical continuityof walls of tunnels of the multiplier A and multiplier B must besatisfied in all modifications of this embodiment of invention.

It should be understood that the electron multiplier MB in which thepath of tunnels is angulated may be used also for X- ray imageintensifiers. For this application it must be constructed to satisfy therequirement that the apex of angulation of the tunnel cannot be higheror lower than 1.0 mm. from the level of the entrance aperture of thistunnel. Another basic requirement is that the exit apertures of themultiplier 80B cannot deviate which means cannot be higher or lower thanthe apex of angulation of the tunnels by more than 1 mm.

Another requirement which has to be satisfied in X-ray imageintensifiers of this type, is that the entrance apertures 81a and exitapertures 81b which belong to the same tunnel, regardless ofconfiguration of said tunnel such as 6, M, dlld or modifications cannotbe displaced by more than 1 mm. in relation to each other. Thisdisplacement means that deviation of the exit aperture from the level ofthe input aperture of the same tunnel cannot exceed 1 mm. The sameapplies to the limits of such deviation of the entrance (input) aperture81a in relation to the exit aperture Mb in straight tunnels 5.

In addition when using such devices for the X-ray image intensifiers theinput end face and the output end face of the electron multiplier 5 or80 or 808 or their modifications, which means the end face provided withthe entrance apertures fllla and the output end face which means the endface provided with exit apertures 81b must be substantially of the samesize as the X-ray reactive means such as composite photocathode 22 orother types. Furthermore electron multiplying device 5, 80 or 80B andtheir modifications must be mounted coaxially with X'ray reactive meanssuch as the composite photocathode 22 or other types.

The reasons for such specific limitations in construction of X-ray imageintersifiers are as follows.

It was found that the use of curved channel multiplier device fit) or $3or 808 and their modifications in X-ray image intensifiers caused income cases an unexpected loss of definition and contrast of images ascompared with the use of straight tunnels of the same diameter. Thereason for this complication was found to be the effect of discreteX-ray pencils of radiation corresponding to individual image pointswhich strike not only the tubular member corresponding to one of saidX-radiation pencils but also the adjacent tubular members.

It was found that in spite of the use of X-ray reactive means such asX-ray sensitive screens or photocathode mounted on the outside or in theinside of X-ray image intensifier tube, a great part of X-ray radiationis not absorbed by such means but is transmitted through them andstrikes the electron multiplier device which is in the path of saidtransmitted Xray beam.

It was found that the part of curved channel multiplier device fill or83 or mm and their modifications which presented the biggest deviationfrom the straight line or curve in longitudinal axis was impinged notonly by one X-ray pencil corresponding to one image point of theexamined body but also by other X-ray pencils corresponding to adjacentimage points. It follows that the construction of the electronmultiplier device of curved type fit) or $3 or angulated type ass mustbe designed to prevent such overlapping by said discrete X-ray pencils.This problem cannot be solved by limiting the diameter of the tunnels asit was practiced in using straight tubular members. The solution of thisproblem is to correlate the definition necessary for X-ray images withthe maximum radius file of curvature of the curved members fill ordeviation from the straight line of their longitudinal axis. it wasfound that the size of the radius fill cof the curvature of tubularmembers fill or deviation from the straight line must not exceed 1 Inaddition when using electron multiplier devices for the X- ray imageintensifiers the input end face of the electron multiplier f or 80, MBor their modifications, which means the end face provided with theentrance apertures Ma, and the output end face which means the end faceprovided with exit apertures 8111 must be substantially of the same sizeas the X- ray reactive means such as the composite photocathode 22 orother types. Furthermore electron multiplying device 5, $0 or MB andtheir modifications must be mounted coaxially with the X-ray reactivemeans such as photocathode 22. It was found that if these two conditionsof construction are not satisfied the image will be destroyed.

In addition in electron multipliers of the type MB which are constructedof two multipliers A and B, as described above it was found thatseparation of the multiplier A and B from each other will damage thedefinition of images because the angular spread of secondary electronswhich exit from the exit aper' tures of the multiplier A is of suchdegree that said electrons cannot be refocused again to enter into theentrance apertures of corresponding tunnels of the multiplier B.

All image tubes may be further improved by construction shown in FIG.211. In all image intensifiers or converters which use a semitransparentphotocathode or photoemissive type like 2, 22, 26 or its modificationsa. large fraction of light passes through the photocathode and is lostfor imaging, in addition it also causes damaging reflections oftransmitted light from walls and electrodes of the tube back to thephotocathode which reduces the contrast of images and reduces the signalto noise ratio of the whole device. The solution of this problem isshown in FIG. 211 in which the light transmitted through thephotocathode 2 and its modifications is utilized now efficiently by thenovel electron multiplier which may have straight tunnels such asmultiplier 5 or which has curved or angulated tunnels such as inmultiplier or 808, which have been described above.

The novel electron multiplier 50 and its modifications described aboveare constructed of fiber-optic plates such as were described above forthe input end wall or output end wall of intensifier tubes and wereillustrated e.g. in FIG. 3 0r used within the image intensifier asillustrated in FIG. I3. The fiberoptic plate 12 or 1120 in thisembodiment of invention is leached out to remove only the inside part ofthe core of fibers and to provide thereby tunnels 50a and walls 46. Aphotoemissive material such as CsOAg or CsSb or multialkali antimonytype is evaporated into said tunnels 50a which may be straight or mayhave configuration of tunnels b and fill or bid to provide the coating 2on their surface which has both photoemissive and secondaryelectron-emissive property as was described above. In this embodiment ofinvention shown in FIG. 2B the walls of each tunnel 5dr: are formed byglass, plastic or other material which is transparent to imagingradiation which has a high index of refraction and which represents theremaining unleached part of the original core of fibers. In additioncoating means are mounted on the external surface of said walls as. Eachof fibers is provided with its own coating means. Such coating meansshould be of material of a lower index of refraction. The thickness ofcoating means of a lower index of refraction should be of a few micronsonly as was explained above, if the walls td are thick enough to havethe necessary mechanical strength. If the walls or their modificationsare of the thickness of less than 5I0 microns, the thickness of thecoating mans may be increased to compensate for the mechanical strength.Such coating means as was described above must also comprise lighbopaquematerial which preferably should be spaced apart from the interfacebetween the core and coating means, so that said interface regionremains light transparent. In another alternative the lightimperviousmaterial may be mounted on and around the outside surface of coatingmeans and may be in the form of an extremely thin layer of black glassor of aluminum or other metal and of the thickness of a fraction of 1micron only and not exceeding 1 micron. It was found that a good opticalinsulation of each of tunnels 50a or their modifications from adjacenttunnels is a very critical requirement. Without the use of theabove-described light-opaque means the image will be destroyed by thelight leaking from one tunnel to adjacent tunnels. It should beunderstood that the use of the light-opaque material in any 'form doesnot eliminate another critical requirement which is the presence of thecoating means of a lower index of refraction than the core as it wasdescribed above.

If the electron multiplier 50 has straight tunnels, the fibers formingthe array or plate may be united together with vacuum-compatible plasticmaterial such as silicones or other fluxes or binders such as glasses ormay be united together to each other directly by their own coatings byheating them.

The use of own individual coatings for each fiber of a lower index ofrefraction and mounted before fusing them together to each other is avery important feature of this embodiment because it produces arrayswhich are capable of much higher resolution and which have a betterlight efficiency due to their lower "packing factor," as compared witharrays in which the fibers do not have own coatings and are united by aminterposed binder or flux of a lower index of refraction instead ofusing individual coating means described above.

In some cases the binder or flux may be added between the individuallycoated fibers. It may be done to facilitate the construction of curvedtunnels from the originally straight tunnels. This is accomplished byforming first an array of straight tunnels and by subjecting such arrayto a lateral pressure while keeping the fiber-optic array at thetemperature at which the walls of tunnels,coating means and of theintervening binding material soften adequately. The use of bindingmaterial does not obviate theneed for own which means individual coatingmeans of a lower index of refraction for each fiber and it is to beunderstood that the use of such owncoating means for each fiber isnecessary in all embodiments of the invention.

The photocathode 2, 22 26 or its modifications may be mounted in aspaced relation to the electron multiplier 50 or 80 or 808 or may bemounted directly on the input end face of said multipliers. In case ofelectron multiplier 50 however if the photocathode is mounted in aspaced relation, such spacing is very critical and cannot exceed 0.1 mm.as otherwise too great loss of resolution of image will occur. This isdifferent from the spacing permissible when relying only on thephotoelectron beam from the photocathode e.g. in case of multipliers 80,in which case the spacing may be many times larger without a great lossof resolution. The mounting of the photocathode 2 or its modificationsin contact with the input end face of the electron multiplier causeshowever short circuiting of the photoelectrons by the electricallyconducting layer 7b on which the photocathode 2 must rest.

In applications which require ruggedness, the photocathode 2 or 22 orits modifications, if mounted on the input end face of the electronmultiplier proved to be too fragile, even after strengthening it by asuperimposed light-transparent layer of silicon oxide or aluminum oxide.In such applications the photocathode 2 must be mounted on the end wallof the intensifier tube or on a separate supporting member which istransparent to image-forming radiation. As was explained above theseparation of the photocathode 2 from the input end face of the electronmultiplier causes loss or resolution. For the best resolution thephotocathode should be in contact with the input end face of theelectron multiplier. It was found however that such contiguousrelationship cases unexpected loss of sensitivity. The cause of it wasfound in the low velocity of photoelectrons which have the energy ofonly I to volts and in the range micron-spectrum of 0.8 micron-1.4micron much less than 1 volt. Such photoelectrons of low energy cannotproduce secondary electrons and will be lost for the image production.It is necessary therefore to accelerate photoelectrons from thephotocathode 2 before they will strike the walls of tunnels 5, 50a 81,81d or their modifications. The

photoelectrons in order to be able to produce secondary electrons musthave energy of 40-80 volts before they strike the walls of tunnels. Thisacceleration is obtained by difference of electrical potential betweenthe photocathode and the entrance apertures of the electron multiplier.The need for this electrical potential gradient controls the minimumspacing, permissible from the efficiency point of view between thephotocathode and input end face of electron multiplier. On the otherhand the need for good resolution controls the maximum spacing possiblebetween the photocathode and the input end face of electron multiplier.It was found that such spacing should be not smaller than 10 microns andnot larger than 25 microns for light images of infrared images as it isshown in FIG. 21a.

These conditions are especially important in case of curved tunnels 81or angulated tunnels 81d because their slanted course interceptsentering photoelectrons close to the entrance aperture of said tunnels.

The use of photoemissive materials such as CSOAg or CsSb or multialkaliphotocathode such as KNaCsSb which are electrically semiconductingmaterials may eliminate the need for semiconducting properties of wallsof tunnels 6 or 50a or curved tunnels 81 or of angulated tunnels 81d.The walls may be now either of semiconducting or of dielectric glasswhich depends on the amount of electron current to be drawn from thetunnels. In case the photoemissive material is not semiconductingelectrically, the walls of tunnels must be electrically semiconductingto provide potential gradient along the tunnels. Lead oxide glasseswhich were rendered electrically semiconducting ducting by hydrogentreatment were not suitable for the embodiment of the electronmultiplier 50a because of their opaqueness, which negated the internalreflection of transmitted light. The present photoemissive photocathodesare extremely transparent'to radiations above 8,000 A. The transmittedlight through the photoemissive photocathode may amount in case of CsOAgto 99 percent of the original incident light in the infrared region ofspectrum. The above-described embodiment of invention is therefore ofspecial importance for devices operating in this range of spectrum as itpermits retrieval and utilization of more than 50 percent of saidtransmitted light and improvement of sensitivity of such devices by thefactor of 10 to 100. In this embodiment of invention e.g. intensifier or95a the walls of tunnels 50a, 81 or 81d must be of material highlytransparent to the light radiation in 0.8 to 1.4 micron range ofspectrum. It was found that the special infrared transmitting glassessuch as AsSe or AsSeTe or Sb S are not transparent enough in this rangeof spectrum. The best results in this part of spectrumwere obtained withsilicate glasses with rare earth elements such as lanthanum or terbiumfor the walls of tunnels because of their high index of refraction. Thecoating materials of a lower index of refraction and suitable for thisrange of spectrum are borosilicate glasses or magnesium fluoride,cryolite, calcium fluoride or germanium oxide. Also light flint glassescan be used for this purpose.

The germanate glasses such as Corning 9572 or 0160 may be used eitherfor walls or for coatings of walls which must have a higher index ofrefraction than said coatings. The same applies to aluminatc glassesespecially to calcium aluminate glasses such as Bausch or Lomb RlR2 orl0, l1, 12 or 20.

Another expedient to provide a better retrieval of light transmittedthrough the photocathode is to provide an oblique configuration betweenthe photocathode 2, 26 or 22 and the input end face of the electronmultiplier 50 or its modifications. This can be accomplished by tiltingthe position of the whole electron multiplier 50 in relation to thephotocathode or instead by tilting the position of photocathode 2 or byproducing tunnels 50a 81 or 81d which run diagonally.

The input end face of the electron multiplier 50 or its modificationsand the output end face of said electron multiplier are both providedwith an electrically conducting layer 7b which leaves the entranceapertures 51 and exit apertures 51a uncovered as was described above.The layer 7b on the input end face must be transparent to imaging lightand may be of tin oxide or of one of metals such as tungsten or platinumof a very thin construction. The input conducting layer 712 and theoutput conducting layer 7b are connected to the source 84 of electricalpotential which must be of unidirectional type and may be of a steady orof pulsating type. The output of the electron multiplier 50 or or 80Bmay be reproduced in the same intensifier tube 95 or 95a or itsmodifications as a visible image on a fluorescent screen 8 or may beconverted into a charge image in a target 30 of television tube or intoelectrical signals or video signals by various modifications of theinvention described above.

The great improvement possible by this construction is due not only tothe increased sensitivity of novel image intensifier 95 or 95a or theirmodifications but to their much higher signal-to-noise ratio thanpossible in the present devices. The transmission of imaging lightthrough the photocathode 2 or its modifications results into the loss ofimage information which cannot be retrieved no matter how great is thesubsequent image intensification. The novel construction regains thelost information and provides therefore a much higher signal-to-noiseratio even if a much lower degree of intensification is used.

Because of this higher signal-to-noise ratio, the intensification by theelectron multiplier 50a or its modifications may be limited to the useof voltage as low as l00500 volt on the input and output end face ofsaid electron multiplier and 1000 volt on the image-reproducing screen.As a result the intensifier 95 or 95a will require much smaller supplyof electrical energy and may be extremely small. This embodiment ofinvention will be especially useful for electronic binoculars or forelectronic goggles which can be worn by the user. The frame of goggleswill support one of such intensifiers for each eye. The electronmultiplier 50 may be reduced in length to O.l-O.5 mm. because its lengthmay be limited to the path of a few passes of light through tunnels 5011by internal reflection. The shortened length of tunnels 50a will permita better and more uniform deposition of coating 2 by evaporation than itwas possible with much longer tunnels used in present devices. Ifadditional intensification is desired, then another electron multipliernow of a standard type may be mounted after the multiplier 50 to receivethe electron beam from the multiplier 50 and to intensify it further.

It should be understood that all novel image intensifiers 95, 95a ortheir modifications may be provided with fiber-optic end walls 12 on theinput side of the tube or on the output side or on both sides as wasdescribed above.

The admission of light photons transmitted through he photocathode intothe walls of tunnels 50a, 6 or M or 81d depends on the index ofrefraction of the walls 46 of the remaining core of fibers and on theindex of refraction of the adjacent coating means. The cone ofacceptance of light into walls 16 of tunnels 500 will be larger if theindex of the core is as high as possible in relation to that of coatingmeans.

The fiber-optic end wall on the input side may be also con structed tolimit the angle of acceptance of incoming radiation if necessary byreducing the difference between the index of refraction of the walls 46and coating means d7. If the difference of said both indices ofrefraction is selected to support the propagation of a selected modewhich means of a selected group of frequency of electromagnetic waves,the end wall will act then as a filter admitting only said selectedwavelengths of radiation.

All novel image intensifiers 95 or 95a or their modifications may beused for imaging of X-rays, neutrons or other invisible radiations byusing a photocathode 2, 22, 26 and modifications or a screen sensitiveto such radiations as was described above.

A serious problem in all imageintensifier tubes is the presence of noisewhich increases strongly at voltages above ltv. The reduction of voltageis not always possible because it causes loss of luminosity ofreproduced image on the fluorescent screen. The solution of this problemis shown in embodiment of invention illustrated in FIG. 22. The novelconstruction shown in the image intensifier 87 may be used for all imageintensifiers described herein both for visible and invisible radiations;and also for all image intensifiers provided with a fluorescentimage-reproducing screen regardless whether they make the use ofelectron multiplier device or not.

The image intensifier 87 is provided with a lightor infrared-sensitivephotocathode 2 or with X-ray-sensitive photocathode 22 or withneutron-sensitive composite photocathode such as 86-24-26. Suchphotocathodes may be mounted on the input end wall 130 of theintensifier tube $7 or on a separate supporting member mounted in aspaced relationship to the end wall 130. The visible or invisible imageis converted by respective photocathode into a beam of electrons havingthe pattern of said image and is focused by electrostatic 1124 ormagnetic focusing means or by proximity focusing on the input aperturesof the electron multiplier 5, 50, d0 or their modifications.

The image intensifier 87 is provided with a fluorescent screen 123 whichis mounted not on the end wall 8dr: as was the fluorescent screen b butin a close but spaced relationship to said end wall Mia. The internalsurface of the end wall 88a is coated with a light-transparentelectrically conducting layer 88b such as of tin oxide, cadmium oxide orof a very thin metal such as tungsten or gold. The conducting layer 88bis connected to an outside source M of unidirectional electricalpotential. Between the exit apertures bllb of electron multiplier 5, 50,80, B or their modifications and the electrically conducting layer ddbis mounted a supporting forarninous plate which comprises atwo-dimensional array of holes 1121 providing passages through saidplate.

The foraminous supporting member 120 may be constructed in the form of asolid plate in which an array of holes is made with a predeterminedspacing between each other. In another embodiment the supporting member120 may be constructed of a mesh screen the holes of which willcorrespond to the holes or apertures of the solid plate. The term plateused in description and in the appended claims is meant to embrace boththe solid-plate support and the mesh-screen support.

The plate 120 should be preferably of a light-opaque material such asblack glass or light-opaque plastics which are compatible with a vacuumtube such as black silicones, sulfones or fluorocarbons.

The plate 120 may be of light-transparent material if the conductinglayer 122 is light opaque but it was found that it is not suitablebecause the conducting layer 122 being extremely thin such as 0.1 to 1micron may develop pinholes which will permit bacltscatter offluorescent light to the photocathode or to electron multiplier device.

The plate 120 should be preferably of dielectric material to preventlateral leakage of electrons of the beam transmitted through holesll2ll.

if the plate 120 is made of electrical conducting material the holest2]! may be preferably coated with an insulting layer but they may beused without insulating layer also. On the surface of the plate ll20which is facing the conducting layer 8% is deposited a fluorescent layer1123 of one of electron-sensitive phosphors. The layer 123 is not acontinuous layer but a mosa ic layer as it is deposited only between theholes 121 and leaves the holes unobstructed for the passage ofelectrons. 0n the opposite surface of plate 120 which faces the electronmultiplier 5 or $0 is mounted a continuous light-impervious andelectrically conducting layer ll22 which may be aluminum.

The layer 122 is connected to the source of electrical potential of DCtype and is provided with positive voltage of energy necessary accordingto application. If the plate 120 is made of electrically conductingmaterial the layer 1122 may be of a dielectric material but it must bealways thin enough to be transmitting to electrons and in addition lightimpervious to prevent the bacltscatter of the fluorescent light fromlayer 123

1. A vacuum tube for the intensifying of X-ray images formed by a beamof X-radiation comprising a plurality of pencils of said X-radiation,each of said pencils corresponding to one image point, said tubecomprising in combination X-ray-reactive means absorbing a part of saidradiation and converting into a beam of electrons having the pattern ofsaid X-radiation image, an electron multiplying device, said devicereceiving said beam of electrons and also the part of X-radiationtransmitted through said X-ray-reactive means, said electron-multiplyingdevice comprising a plurality of separate individual empty tunnels, saidtunnels having entrance apertures for the entrance of said beam ofelectrons and exit apertures for the exit of electrons, said tunnelshaving configuration of the longitudinal axis between said entrance andsaid exit apertures in which lateral deviation from a straight line, isnot exceeding 1 mm. and preventing each of said X-ray pencilscorresponding to individual image points from impinging on more than oneof said hollow tunnels during the passage through saidelectron-multiplying device, said vacuum tube comprising furthermoremeans for receiving and utilizing said beam of electrons exited fromsaid apertures, in said device furthermore the difference of the levelof said exit apertures in relation to the level of said entranceapertures not exceeding 1 mm.
 2. A device as defined in claim 1, whichcomprises in addition means producing pulses of unidirectionalelectrical potential and connected to said electron-multiplying device.3. A device as defined in claim 1, in which the end wall of said tubecomprises a two-dimensional array of light-conducting members, saidmembers having a core of material of a high index of refraction andprovided with coating means of a lower index of refraction than saidcore and having the thickness not exceeding a few microns, saidprecoated members united together and conducting light by internalreflection.
 4. A vacuum tube as defined in claim 1, in which saidelectron-multiplying device comprises plurality of individual hollowmembers united together, and in which said vacuum tube comprisesfurthermore a screen for receiving said exited electrons and animperforate and electron-transmitting member mounted between said X-rayreactive means and said screen and spaced apart from said screen.
 5. Avacuum tube as defined in claim 2, in which at least two of saidelectron-multiplying devices are mounted adjacent to each other.
 6. Adevice as defined in claim 2, in which said electron-multiplying devicecomprises plurality of individual hollow members united together, and inwhich said vacuum tube comprises furthermore a screen for receiving saidexited electrons and an imperforate and electron-transmitting membermounted between said X-ray-reactive means and said screen and spacedapart from said screen.
 7. A device as defined in claim 3, in which atleast two said electron-multiplying devices are mounted adjacent to eachother.
 8. A device as defined in claim 4, in which saidelectron-multiplying device comprises plurality of individual hollowmembers united together.
 9. A device as defined in claim 3, in which atleast two said electron-multiplying devices are mounted adjacent to eachother.
 10. A device as defined in claim 8, which comprises fluorescentmeans.